(+ small cosmetic fixes)

All instances in the wild have now moved their DB
from srv/res6stnet/registry to srv/re6stnet.

See commit a1ed9c30.

Fallback to alternate-url only happens on HTTPError.

SSL certificate of people.redhat.com has bad chain, which results with failed
downloads.

mysql: With universal_newlines, python3 subprocess assumes that communicate() parameter is str() (not bytes()).

But mysql_script_file was opened as a binary files and thus a bytes() was returned:
    File "etc/run/mariadb_update", line 51, in <module>
      sys.exit(slapos.recipe.generic_mysql.mysql.updateMysql(mysql_upgrade_binary='/srv/slapgrid/slappart3/bin/mysql_upgrade', mysql_binary='/srv/slapgrid/slappart3/bin/mysql', mysql_script_file='/srv/slapgrid/slappart3/etc/mariadb_initial_setup.sql'))
    File "parts/slapos.cookbook-repository/slapos/recipe/generic_mysql/mysql.py", line 31, in updateMysql
      result = mysql.communicate(mysql_script)[0]
    File "parts/python3/lib/python3.7/subprocess.py", line 964, in communicate
      stdout, stderr = self._communicate(input, endtime, timeout)
    File "parts/python3/lib/python3.7/subprocess.py", line 1692, in _communicate
      self._save_input(input)
    File "parts/python3/lib/python3.7/subprocess.py", line 1774, in _save_input
      self._input = self._input.encode(self.stdin.encoding,
  AttributeError: 'bytes' object has no attribute 'encode'

See merge request nexedi/slapos!1135

Using macros.cfg to add a new macro.
This macro will works like [macro-virtual-env].
Neverthless, it will use pygolang to create a more "classic" interpreter.

Use the python `six` library to realize the compatibility of `urlparse` in python2 and python3

See merge request nexedi/slapos!1138

See merge request !1128

Since da03653908aea9a62f805faf0328f7b2f046abaa slapos.core's slapproxy transmit
more parameters, so adapt tests to account for it.

The https://bz.apache.org/bugzilla/show_bug.cgi?id=65769 seems hitting
various software releases with strace like:

select(0, NULL, NULL, NULL, {tv_sec=1, tv_usec=0}) = 0 (Timeout)
wait4(-1, 0x7ffe9579eb84, WNOHANG|WSTOPPED, NULL) = -1 ECHILD (No child processes)
times({tms_utime=561, tms_stime=669, tms_cutime=558, tms_cstime=99}) = 3280801757

Also adapt the --with-pcre switch in order to find the pcre-config during the
build process.

This prevents errors like:

Error while executing:
/srv/slapgrid/slappart54/t/dau/shared/git/f7efae57344573a59b9e441431a34e9a/bin/git ls-remote -h -t git://github.com/qunitjs/node-qunit.git

fatal: remote error:
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.

In slapos.core commit 425f5bb7b (slapgrid: replace platform.linux_distribution()
with distro.linux_distribution(), 2022-03-21), a dependency to distro
was introduced. Because tests run with slapos.core fetched from git, they
already started to fail because of the missing version pin.

The pin is made to the latest version for both python2 and python3.
Usually we take the latest version compatible with python2, but I just
thought this way was probably better.

I think we don't want trailing whitespaces anywhere in this repository

This reverts commit e1dae860.

Despite of microupgrade, there are problems with compiling this version.

Via header for response and request is fully stabilized and present according
to the RFC now.

Important information, like protocol and protocol version are exposed.

Hops which were present in the request are stored and descriptively named.

Versions of components are exposed in hidden way and in the same time the
frontend administrator and frontend user are able to analyze the versions,
and the version history present on the node is transmitted back.

Additionally each node can be identified by frontend admins and users for
request and response headers, allowing more debugging.

Improve the tests by extending assertSlaveBase and reuse it instead of
duplicating the code everywhere.