Factor-out the driver to run_nxdtest in a separate thread done in
0ad45a9c (Detect if a test leaks processes and terminate them) from
test_run_procleak into run_nxdtest, so that all tests are run this way
for pytest.timeout, if requested, to work universally for all tests.

The logic of how we run nxdtest under tests and handle timeout will be,
hopefully, soon reworked more, but it is anyway good to keep this logic
in only one place.

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!14

A user might cancel test result in ERP5 UI if e.g. some misbehaviour is
detected and a new revision is ready to be tested. This works by
test_result.start() returning None - indicating that there is no more
test_result_lines to exercise. Master also indicates this cancellation
via test_result.isAlive() returning False, but until now we were not
using that information and were always waiting for completion of current
test job that is already spawned.

This works well in practice if individual tests are not long, but e.g.
for SlapOS.SoftwareReleases.IntegrationTest-* it is not good, because
there an individual test might takes _hours_ to execute.

-> Fix it by first setting global context to where we'll propagate
cancellation from test_result.isAlive, and by using that context as the
base for all other activities. This should terminate spawned test
process if test_result is canceled.

The interval to check is picked up as 5 minutes not to overload master.
@jerome says that

    We now have 341 active test nodes, but sometimes we are using
    more, we did in the past to stress test some new machines.

    For the developer, if we reduce the waiting time from a few hours to 1
    minutes or 5 minutes seems more or less equivalent.

For 350 testnodes and each nxdtest checking its test_result status via
isAlive query to master every 5 minutes, it results in ~ 1 isAlive
request/second to master on average.

Had to change time to golang.time to use time.after().
Due to that time() and sleep() are changed to time.now() and
time.sleep() correspondingly.

/helped-and-reviewed-by @jerome
/reviewed-on nexedi/nxdtest!14

This is normal rule to return an error from a task if the task has to
abort due to cancellation. We already do this in tee, but not in the
function that is waiting for spawned process to complete(*).

-> Fix that. Wrap corresponding wg.wait() into try/except and check if
it fails due to cancellation, upon which we should not raise, but
instead should continue to finish current test_result_line and only
after stop test run normally (again without raise, but with regular one
line log entry).

(*) added in 0ad45a9c (Detect if a test leaks processes and terminate them)

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!14

In 0ad45a9c (Detect if a test leaks processes and terminate them) we
organized waiting for spawned processes with handing ctx and sending
SIGKILL to the main spawned process on ctx cancel even though other
leaked processes are always first sent with SIGTERM and - only after
shutdown timeout - later with SIGKILL.

This is too brutal. Rework the code to first send SIGTERM to the main
spawned test process too, and leverage SIGKILL only later after shutdown
timeout.

This will be tested in a later patch which exercises how cancel from
master is propagated.

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!14

Also log if master told us that we have nothing to do, and if the mode to run is local.

This should make it a bit more clear what is going on just by looking at
nxdtest log. See previous patch for more details and context.

For the reference: here is how updated output looks like in the normal case:

    date:   Thu, 09 Dec 2021 04:20:37 CET
    xnode:  slapuser7@rapidspace-testnode-001
    uname:  Linux rapidspace-testnode-001 4.9.0-16-amd64 #1 SMP Debian 4.9.272-1 (2021-06-21) x86_64
    cpu:    Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz
    # running for test_result_module/20211209-170FD3998

    >>> pytest
    $ python -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /srv/slapgrid/slappart7/t/dfp/soft/47cc86af27d234f0464630f2a0d22a6f/parts/zodbtools-dev
    collected 46 items

    zodbtools/test/test_analyze.py .                                         [  2%]
    zodbtools/test/test_commit.py ..                                         [  6%]
    zodbtools/test/test_dump.py ...                                          [ 13%]
    zodbtools/test/test_restore.py ..                                        [ 17%]
    zodbtools/test/test_tidrange.py .............................            [ 80%]
    zodbtools/test/test_zodb.py .........                                    [100%]

    ========================== 46 passed in 9.15 seconds ===========================
    ok      pytest  12.433s # 46t 0e 0f 0s
    # ran 1 test case:  1·ok

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!15

Nxdtest logs system information (bd91f6f1 "Include system information
into log output") and run summary at the end (9f413221 "Emit run summary
at the end"). However all that information currently is printed only if
master is successfully connected and actually tells to run the tests.

This behaviour is not very useful, because if nxdtest log output on
testnode is empty, it is not clear - whether it was "we have to do
nothing", or nxdtest stuck somewhere or something else.

For example
https://nexedijs.erp5.net/#/test_result_module/20211208-47D165B7/12 is
currently marked as Running for many long hours already. And the log on
testnode regarding nxdtest run is just:

    2021-12-08 15:42:17,314 INFO     $ PATH=/srv/slapgrid/slappart13/srv/slapos/soft/2956f419073cb2249ed953507fa6b173/bin:/opt/slapos/parts/bison/bin:/opt/slapos/parts/bzip2/bin:/opt/slapos/parts/gettext/bin:/opt/slapos/parts/glib/bin:/opt/slapos/parts/libxml2/bin:/opt/slapos/parts/libxslt/bin:/opt/slapos/parts/m4/bin:/opt/slapos/parts/ncurses/bin:/opt/slapos/parts/openssl/bin:/opt/slapos/parts/pkgconfig/bin:/opt/slapos/parts/python2.7/bin:/opt/slapos/parts/readline/bin:/opt/slapos/parts/sqlite3/bin:/opt/slapos/parts/swig/bin:/opt/slapos/bin:/opt/slapos/parts/patch/bin:/opt/slapos/parts/socat/bin:/usr/bin:/usr/sbin:/sbin:/bin SLAPOS_TEST_LOG_DIRECTORY=/srv/slapgrid/slappart13/var/log/testnode/dgd-xStX9safSG SLAPOS_TEST_SHARED_PART_LIST=/srv/slapgrid/slappart13/srv/shared:/srv/slapgrid/slappart13/t/dgd/shared /bin/sh /srv/slapgrid/slappart13/t/dgd/i/0/bin/runTestSuite --master_url $DISTRIBUTOR_URL --revision slapos=13977-ec686a708633f689382426063c21efbe3b2eab04,slapos.core=8698-91edab77ed36c160da8017cfdc1673fe7a8e10de --test_node_title rapidspace-testnode-008-3Nodes-DEPLOYTASK0 --test_suite SLAPOS-SR-TEST --test_suite_title SlapOS.SoftwareReleases.IntegrationTest-kirr.Python2 --project_title 'Rapid.Space Project'

without anything else.

With this patch nxdtest would print system information and report how many
tests it had run, if its invocation did not stuck.

In this patch we only move code that calls system_info and defer summary log
before code that connects to master. In the following patch we'll add more
logging around connecting to master.

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!15

Sometimes there is zero testcases to be executed on testnodes, and
log output from nxdtest is just

    date:   Wed, 10 Nov 2021 12:31:50 MSK
    xnode:  kirr@deca.navytux.spb.ru
    uname:  Linux deca 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64
    cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz

it is not clear from such output did the run ended or the test got
stuck. After this patch it becomes

    date:   Wed, 10 Nov 2021 12:31:50 MSK
    xnode:  kirr@deca.navytux.spb.ru
    uname:  Linux deca 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64
    cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
    # ran 0 test cases.

And in general, when there are several testcases to be run, it is helpful to
indicate end of such run and to print brief summary of result status for all
ran test cases. Example output:

    wendelin.core$ nxdtest -k test.wcfs
    date:   Wed, 10 Nov 2021 12:35:34 MSK
    xnode:  kirr@deca.navytux.spb.ru
    uname:  Linux deca 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64
    cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
    >>> test.wcfs/fs:1
    ...
    ok      test.wcfs/fs:1  25.035s # 35t 0e 0f 0s

    >>> test.wcfs/fs:2
    ...
    ok      test.wcfs/fs:2  21.033s # 35t 0e 0f 0s

    >>> test.wcfs/fs:
    ...
    ok      test.wcfs/fs:   21.056s # 35t 0e 0f 0s
    # ran 3 test cases:  3·ok

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!12

This parses pylint output with a simple regexp and counts one failure per
message reported.

This has not been tested yet, but we decided to apply this commit already.

/acked-by @kirr
/reviewed-on !11

When using compile with the actual file path, we can have better tracebacks
in case of errors.

before:

    Traceback (most recent call last):
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/bin/nxdtest", line 22, in <module>
        sys.exit(nxdtest.main())
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 142, in main
        tenv = loadNXDTestFile('.nxdtest')
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 75, in loadNXDTestFile
        six.exec_(src, g)
      File "<string>", line 77, in <module>
    NameError: name 'Pylint' is not defined

after:

    Traceback (most recent call last):
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/bin/nxdtest", line 22, in <module>
        sys.exit(nxdtest.main())
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 142, in main
        tenv = loadNXDTestFile('.nxdtest')
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 75, in loadNXDTestFile
        six.exec_(compile(src, os.path.realpath(path), 'exec'), g)
      File "/srv/slapgrid/slappart3/srv/runner/instance/slappart8/var/nxdtest/.nxdtest", line 77, in <module>
        summaryf=Pylint.summary,
    NameError: name 'Pylint' is not defined

/reviewed-by @kirr
/reviewed-in !10

For every TestCase nxdtest spawns test process to run with stdout/stderr
redirected to pipes that nxdtest reads. Nxdtest, in turn, tees those
pipes to its stdout/stderr until the pipes become EOF. If the test
process, in turn, spawns other processes, those other processes will
inherit opened pipes, and so the pipes won't become EOF untill _all_
spawned test processes (main test process + other processes that it
spawns) exit. Thus, if there will be any process, that the main test
process spawned, but did not terminated upon its own exit, nxdtest will
get stuck waiting for pipes to become EOF which won't happen at all if a
spawned test subprocess persists not to terminate.

I hit this problem for real on a Wendelin.core 2 test - there the main
test processes was segfaulting and so did not instructed other spawned
processes (ZEO, WCFS, ...) to terminate. As the result the whole test
was becoming stuck instead of being promptly reported as failed:

    runTestSuite: Makefile:175: recipe for target 'test.wcfs' failed
    runTestSuite: make: *** [test.wcfs] Segmentation fault
    runTestSuite: wcfs: 2021/08/09 17:32:09 zlink [::1]:52052 - [::1]:23386: recvPkt: EOF
    runTestSuite: E0809 17:32:09.376800   38082 wcfs.go:2574] zwatch zeo://localhost:23386: zlink [::1]:52052 - [::1]:23386: recvPkt: EOF
    runTestSuite: E0809 17:32:09.377431   38082 wcfs.go:2575] zwatcher failed -> switching filesystem to EIO mode (TODO)
    <LONG WAIT>
    runTestSuite: PROCESS TOO LONG OR DEAD, GOING TO BE TERMINATED

-> Fix it.

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!9

re.match only find matches where the pattern appears at the beginning of
the string, whereas re.search matches if the pattern appears anywhere in
the string. This is behavior is consistent with pytest, go test and ERP5's
runUnitTest

For more details, see the discussion from !6 (comment 121409)

/reviewed-on: !8

The reason is that with threading.Thread if exception happens in that
spawned thread, this error is not propagated to main driver, while with
sync.WorkGroup an exception from any spawned worker is propagated back
to main. For example with the following injected error

    --- a/nxdtest/__init__.py
    +++ b/nxdtest/__init__.py
    @@ -267,6 +267,7 @@ def main():

     # tee, similar to tee(1) utility, copies data from fin to fout appending them to buf.
     def tee(ctx, fin, fout, buf):
    +    1/0
         while 1:

before this patch nxdtest behaves like ...

    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ nxdtest
    date:   Tue, 24 Nov 2020 14:55:08 MSK
    xnode:  kirr@deco.navytux.spb.ru
    uname:  Linux deco 5.9.0-2-amd64 #1 SMP Debian 5.9.6-1 (2020-11-08) x86_64
    cpu:    Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz

    >>> pytest
    $ python -m pytest
    Exception in thread Thread-2:
    Traceback (most recent call last):
      File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
        self.run()
      File "/usr/lib/python2.7/threading.py", line 754, in run
        self.__target(*self.__args, **self.__kwargs)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero

    Exception in thread Thread-1:
    Traceback (most recent call last):
      File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
        self.run()
      File "/usr/lib/python2.7/threading.py", line 754, in run
        self.__target(*self.__args, **self.__kwargs)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero

    error   pytest  0.583s  # 1t 1e 0f 0s
    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ echo $?
    0

Here the error in another thread is only printed, but nxdtest is not aborted.
Above it reported "error", but e.g. when testing pygolang/py3 and raising an
error in tee it even reported it was succeeding
( !6 (comment 121393) ):

    slapuser34@vifibcloud-rapidspace-hosting-007:~/srv/runner/instance/slappart0$ ./bin/runTestSuite
    date:   Tue, 24 Nov 2020 12:51:23 MSK
    xnode:  slapuser34@vifibcloud-rapidspace-hosting-007
    uname:  Linux vifibcloud-rapidspace-hosting-007 4.19.0-6-amd64 #1 SMP Debian 4.19.67-2+deb10u2 (2019-11-11) x86_64
    cpu:    Intel(R) Xeon(R) CPU E5-2678 v3 @ 2.50GHz

    >>> thread
    $ python -m pytest
    Exception in thread Thread-1:
    Traceback (most recent call last):
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 926, in _bootstrap_inner
        self.run()
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 870, in run
        self._target(*self._args, **self._kwargs)
      File "/srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/nxdtest/nxdtest/__init__.py", line 268, in tee
        fout.write(data)
    TypeError: write() argument must be str, not bytes

    ok      thread  9.145s  # 1t 0e 0f 0s

    >>> gevent
    $ gpython -m pytest
    Exception in thread Thread-3:
    Traceback (most recent call last):
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 926, in _bootstrap_inner
        self.run()
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 870, in run
        self._target(*self._args, **self._kwargs)
      File "/srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/nxdtest/nxdtest/__init__.py", line 268, in tee
        fout.write(data)
    TypeError: write() argument must be str, not bytes

    ok      gevent  21.980s # 1t 0e 0f 0s

After this patch nxdtest correctly handles and propagates an error originating
in spawned thread back to main driver:

    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ nxdtest
    date:   Tue, 24 Nov 2020 14:54:19 MSK
    xnode:  kirr@deco.navytux.spb.ru
    uname:  Linux deco 5.9.0-2-amd64 #1 SMP Debian 5.9.6-1 (2020-11-08) x86_64
    cpu:    Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz

    >>> pytest
    $ python -m pytest
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/venv/z4-dev/bin/nxdtest", line 11, in <module>
        load_entry_point('nxdtest', 'console_scripts', 'nxdtest')()
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 230, in main
        wg.wait()
      File "golang/_sync.pyx", line 237, in golang._sync.PyWorkGroup.wait
        pyerr_reraise(pyerr)
      File "golang/_sync.pyx", line 217, in golang._sync.PyWorkGroup.go.pyrunf
        f(pywg._pyctx, *argv, **kw)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero
    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ echo $?
    1

NOTE sync.WorkGroup requires every worker to handle context cancellation, so
that whenever there is an error, all other workers are canceled. We add such
cancellation handling to tee but only lightly: before going to block in
read/write syscalls we check for whether ctx is canceled or not. However the
proper handling would be to switch file descriptors into non-block mode and to
select at every IO point on both potential IO events and potential
cancellation. This is left as TODO for the future.

/reviewed-on !7

These are the necessary changes to run `SlapOS.Eggs.UnitTest-*` and `SlapOS.SoftwareReleases.IntegrationTest-*` using nxdtest

See merge request !6

/reviewed-by @kirr

If test program output on stderr (which is unbuffered), the
output of the test program will appear before output from nxdtest
advertising the program that is about to be executed, because nxdtest
stdout is buffered (testnode does not set PYTHONUNBUFFERED, and eventhough
nxdtest sets PYTHONUNBUFFERED in its own environ, this only applies to sub
processes)

While pytest sends everything in stdout, some other programs send on stderr.

While treating output as text would not really be impossible, treating it
as bytes seems a better choice because:
 - we don't have to make assumptions about what output encoding the test
   program is using for output
 - `tee` can just read stream output bytes by bytes without having to worry
   about multi-bytes characters
 - testnode protocol uses xmlrpc.client.Binary, which uses bytes.

Because using bufsize=1 implies reading subprocess output as text, we use
bufsize=0 instead in the subprocess.Popen call, to prevent buffering.

To make manipulation of strings and bytes easier, we add a dependency on
pygolang, so that we can use its strings utility functions.

Also add a few tests to verify general functionality.

For example wendelin.core 2 uses pytest_unconfigure to unmount wcfs
servers that it spawned:

https://lab.nexedi.com/kirr/wendelin.core/blob/1be4d730/conftest.py#L27-53

This usually leads to some test as shown in added test.

-> Skip that text backwards and actually detect pytest summary line
instead of returning empty dict, because empty dict forces Nexedi ERP5
to treat such test run to have UNKNOWN status, e.g.

https://erp5.nexedi.net/test_result_module/20201108-C170850/11

/cc @jerome
/reviewed-on nexedi/nxdtest!5

This allows to establish tests for Nxdtest itself under Nexedi testing
infrastructure.

/cc @jerome
/reviewed-on nexedi/nxdtest!4

lab.nexedi.com/kirr/nxdtest -> lab.nexedi.com/nexedi/nxdtest

nexedi/slapos!839 (comment 119120)
nexedi/slapos!839 (comment 119142)

/cc @jerome
/reviewed-on nexedi/nxdtest!3

/cc @jerome
/reviewed-on nexedi/nxdtest!1

Verify pytest summary-parsing functionality.

Create real nxdtest module, so that things could be imported from there.
As the result switch `nxdtest` program from scripts to entry_point.

Here is e.g. corresponding summary:

    ===== 12 failed, 14 passed, 4 xfailed, 12 error in 19.58 seconds =====

When checking logs on testnode, it is very useful to know which kernel
version is running inside (wendelin.core uses FUSE and depends on having
patched FUSE module for kernels < 5.2), which CPU is there, etc.

Format of printed output follows go benchmarking format and coincides
with start of `neotest info-local` (see footers on figures in
http://navytux.spb.ru/~kirr/neo.html and here:
https://lab.nexedi.com/kirr/neo/blob/1f26678b/go/neo/t/neotest#L585-874)

- To list which tests are in there,
- To execute only selected tests.

Apply only to local mode.
Very handy for debugging.

We started to print test result summary line for a testcase run since
0153635b (Teach nxdtest to run tests locally). However it is not present
in log when nxdtest is run under master. -> Include summary lines
everywhere for uniformity, with reason similar to bd1333bb (log += title
and argv for ran testcase).

This reverts commit 34e96b1d. Reason for revert is that since bd1333bb
(log += title and argv for ran testcase) we always emit details of
to-be-run command to log in the beginning of testcase run.

We started to display command and envadj in the log in the previous
patch. However only command - without envadj - was reported to master
for test result. -> Make it uniform: include envadj into details
everywhere.

When there are several or many testcases, it is hard to understand - by
seeing just log or console output - which part of the test suite was
running. It also helps to see the exact command that was spawned.

Example output for pygolang. Before:

    (neo) (z-dev) (g.env) kirr@deco:~/src/tools/go/pygolang$ nxdtest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ssssss.sssssss                                   [100%]

    ==================== 99 passed, 13 skipped in 5.42 seconds =====================
    ok      thread  5.656s  # 112t 0e 0f 13s
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ..............                                   [100%]

    ========================= 112 passed in 17.35 seconds ==========================
    ok      gevent  17.768s # 112t 0e 0f 0s

After:

(neo) (z-dev) (g.env) kirr@deco:~/src/tools/go/pygolang$ nxdtest

    >>> thread
    $ python -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ssssss.sssssss                                   [100%]

    ==================== 99 passed, 13 skipped in 5.27 seconds =====================
    ok      thread  5.508s  # 112t 0e 0f 13s

    >>> gevent
    $ gpython -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ..............                                   [100%]

    ========================= 112 passed in 17.32 seconds ==========================
    ok      gevent  17.729s # 112t 0e 0f 0s

failure is assertion failure.
error is any other error.

Source: https://docs.python.org/3/library/unittest.html#organizing-test-code
-> "If the test fails, an exception will be raised ... identify the test
case as a failure. Any other exceptions will be treated as errors"

While searching ERP5 code for failure_count to clarify its meaning, I've
also discovered expected_failures and unexpected_successes (*) so they
are also added to the table.

(*) see e.g. https://lab.nexedi.com/nexedi/erp5/blob/1e31c091/product/ERP5Type/tests/ERP5TypeTestSuite.py#L6-8

Instead of just traceback saying that e.g. "No such command" without
information which command it was tried to spawn, stderr will now include
what was tried to be run. This makes diagnostic easier.

Many project that use pytest for testing won't need to redefine it over
and over again in their .nxdtest file.

It is very handy to debug both .nxdtest and nxdtest tool itself, and to
be able to run tests locally during development instead of (in addition
to) waiting for the test result from test nodes.

-> Teach nxdtest to run and report tests locally if no --master_url was
provided.

Idea is taken from runTestSuite.in from NEO, Cython+, Buildout and Rina:

https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L95-105
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L55-75
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/stress-testing/runTestSuite.in#L17-37
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/cython-test/runTestSuite.in#L38-58
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/buildout-testing/runTestSuite.in#L21-39
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/build-rina/runTestSuite.in#L29-49

Instead of copying code over and over again, let's stick to UNIX
approach and make it to be in one tool only that does its job
(hopefully) good.

Previously, if --master_url was not provided, the program would crash
with UnboundLocalError for status, since for that case list of tests was
empty. Fix it by moving status initialization higher by one level.

See next patch where we'll add meaning for nxdtest run with no
--master_url set.

It is frequently needed to set some environment variable without
completely resetting everything else in the environment, because that
everything else can carry settings like PATH, PYTHONPATH, RPATH, etc for
the program to be able to run at all.

See nexedi/pygolang@b938af8b for recent example.

After previous patch that summary function is no-longer used, is
specific to NEO/py and so should be defined in .nxdtest file in that
project. lab.nexedi.com/kirr/neo will be adjusted correspondingly.

Make the tool generic: load list of testcases to run from .nxdtest file
and process the correspondingly. See added top-level documentation for
details.

Amends e9cc7e07 (Add minimal packaging setup)