Prepare for upcoming nxdtest changes to run each testcase with its own
/tmp and /dev/shm:

1) put unshare from SlapOS component into $PATH, so that our version is
   used even if OS provides /bin/unshare. As @jerome explains we need
   features that were added relatively recently and are missing in unshare
   on Debian 10: nexedi/nxdtest!13 (comment 146752)

   It is anyway better to "isolate" from OS by using our own component
   instead of system-provided one.

   Correspondingly adjust util-linux to enable unshare in its build.

2) similarly to "1" adjust util-linux to enable mount so that our version
   is used instead of /bin/mount. For example on Debian 9, even if we
   successfully enter user/mount namespace with `unshare -Umc`

       /bin/mount -t tmpfs none /tmp

   complains that

       mount: only root can use "--types" option

   -> Fix it the same way as with unshare by forcing usage of
   SlapOS-provided mount.

3) rework how nxdtest script is generated and split it into .nxdtest.pyexe and
   nxdtest itself. .nxdtest.pyexe is python interpreter via which nxdtest is run.
   This interpreter has all eggs required by nxdtest in sys.path, so that
   nxdtest could spawn its trun.py via sys.executable. If we don't care to have
   properly setup sys.executable, trun.py will fail when importing any module that
   nxdtest.py could already successfully import.

   Initially I tried to workaround this issue via adjusting $PYTHONPATH <-
   sys.path in main nxdtest script, but @jerome points out that, $PYTHONPATH,
   if set, also affects processes that trun.py spawns, which is not good:

   nexedi/slapos!1095 (comment 146799)

   -> so fix this via running nxdtest via environment where sys.executable is
   properly setup python interpreter with path for all eggs that nxdtest has
   access to.

   Because we already have half-way workarounds for similar problem in several
   places, and because running a script with correctly setup sys.executable is
   generally better, I would say it should be a good idea to rework
   zc.recipe.egg:scripts to generate all scripts to work this way, but I do not
   want to fight about it.

   So let's leave this scheme nxdtest-specific for now.

/cc @tomo
/helped-and-reviewed-by @jerome
/reviewed-on nexedi/slapos!1095

When adding a route to an interface not up yet, "ip route" command fails
with:

Error: Device for nexthop is not up.

So we need to up the device before adding the routes.

This is a regression with 0.48 that prevented parts to be shared depending
on which Python is used to run Python (whether it's version 2 or 3).

The patch was useless since version 6.0:
http://ncurses.scripts.mit.edu/?p=ncurses.git;h=6a530b46563470c2ca73579d1994a0c8e275dd98

slapos.core now depends on PyYAML and jsonschema

This upgrade fixes deadlock when new context is created from
already-canceled parent[1]. It also comes with other minor enhancements
and fixes needed e.g. for `zodb restore`[2].

[1] pygolang@58d4cbfe
[2] https://pypi.org/project/pygolang/#pygolang-change-history

json-c, memcached and xpdf are still maintained but current
buildout.cfg are not useful if we want to ship a new version.

Keep compatibility with the default webrunner configuration.

Prevent unexpected instance deletion.

See merge request !1094

It appears no longer needed to use LD_LIBRARY_PATH to ensure the
correct runtime path resolution of libsecret in theia's `keytar`
component. Also LD_LIBRARY_PATH was leaking into theia's environment
and affecting tests launched from within theia.

This reverts commit 681ec188.

See merge request nexedi/slapos!1096

Always format the partitions to ensure the slapformat configuration is
valid, because the constructor overwrites it with invalid values.

We need a valid configuration so that `slapos node format` works,
and we need `slapos node format` for the resiliency import script.

No need for the full URL here

This will force a password reset

Aggregate monitoring URLs from the main theia, clones and PBS.

Also add monitor-setup-url to the parameters published by the PBS.