Remove

```
[gcc:python2]
part = gcc-8.5
```

from neoppod/software-common.cfg and dream/software.cfg as it causes
gcc being pinned to a different version before and after rebootstrap
when the initial python version is not Python2.

This reverts dc91e5d4.

When use-ipv6 is enabled, make mariadb publish an url of the form:
  `mysql://user:password@[ipv6]:port/database`

instead of:
  `mysql://user:password@ipv6:port/database`

which results in the zope instances crashing during processing
due to urlparse.urlsplit failing to parse the url.

Move the versions of matplotlib, matplotlib-inline and cycler pinned in
component/matplotlib/buildout.cfg to slapos.cfg.
The cycler version for Python 3.7 will be upgraded to 0.11.0 as it is
compatible.

One reason motivating this change is that the version of `cycler` in
stack/slapos.cfg is overriding the version specified in
component/matplotlib/buildout.cfg for the erp5-zope2 software release.
This is a problem because the former does not take into account the
Python version, while the later does.
Thus, attempting to compile erp5-zope2 would give the following error:

```
Getting distribution for 'cycler==0.11.0'.
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
ERROR: Package 'cycler' requires a different Python: 2.7.18 not in '>=3.6'
While:
  Installing matplotlib.
  Base installation request: 'cycler', 'python-dateutil', 'numpy'
  Getting distribution for 'cycler==0.11.0'.
```

This adds the right version of `cycler` for Python 2 in `slapos.cfg`, so
that it does not fail.

also use archive.apache.org where the link will not disappear even after the release of newer versions.

also use archive.apache.org where the link will not disappear even after the release of newer versions.

  You cannot expand properties with  since it expects
  to be an object or boolean.

  Revert to use allOf back, however set additionalProperties true,
  so the schemas are mutually partially valid.

  Other solutions might too verbose or too restrictive to the use
  case (or simply invalid).

  Include missing #, update wrong url, missing  definition...

  Don't failover to Draft7 if schema is badly defined or undefined.

  Enforce proper definition and raise nicely if the value is bad or
  unsupported.

  Extra: Fixup the list to follow up json schema specification

After the change in https://lab.nexedi.com/nexedi/slapos.core/-/blob/2b80692d62b3dbd9e67d70d6143f180fc2f155fc/slapos/util.py#L449-453, there is now a KeyError message if the serialisation is not found. The theia test was actively checking there is no "Error" in the output log hence it was now failing.

Allow just this specific error.

  allOf implies that all (both) schemas should be valid, but
    additionalProperties false wont allow it, since it become multually
    invalid. (You can validate only one or None)

  Just use $ref to expand the list, it end up with the expected outcome
   reducing complexity.

  Note: kvm wasn't using additionalProperties false but it was changed
   because it makes it future proof, in case we set it (we should set).

Logs for the whole process shall be formatted in the same way, so define it
once in global section.

Long request lines result with truncated logs, which leads to impossibility to
debug cluster.

Maximize the log lines emitted by haproxy, and follow up this withing
accompanying rsyslogd.

Allow very long, but still much smaller, URI logging.