This does not compile on debian 12

In ubuntu 21.04 (libc6 2.33-0ubuntu5) or current debian testing
(libc6 2.32-5) no longer use open to open /etc/hosts, but what appears
as "openat" in strace output - but can not be replaced by defining an
openat function.

This uses https://github.com/figiel/hosts which uses another approach
of replacing getaddrinfo, gethostbyname* and inet_aton.

Users have been updated a bit, because there are some small differences:
 - the /etc/hosts replacement file is defined by HOSTS_FILE environment
   variable, not HOSTS
 - the library name is libuserhosts.so, not userhosts.so

Other notable differences, for which we did not need code change are:
 - the new library also try to load a file when HOSTS_FILE is not set
 - the new library still use original /etc/hosts file
 - the new library supports aliases to hostnames, not only ip addresses

We can not rely on system python here, it's a bit better to rely on
buildout's python ( the main reason is that it complies with
slapos-sr-testing not having system python ).

The implementation is a bit complicated, we can not just reference
${buildout:executable} in the profile, because doing so will cause an
infinite loop with rebootstrap and software installation never finish
because options of ca-certificates change at every run if they include
the python path. Instead, we use a pre-make-hook to rewrite the Makefile
without saving the interpreter in option. This python is only used
during the build process (to generate the certificate files) and not
used at run time, so it does not really depend on python strictly
speaking. Anyway, because it's a component used very early in the
bootstrap, we can not reference python here.

See !1207 (comment 174788)

This reverts commit 2570ea1d.

We shouldn't change URL in this branch.

This reverts commit 32a838ac.

We shouldn't change URL in this branch.

We want to detect usage of system python2 or python.

Fixes compatibility with glibc >= 2.30 .
Update users to new usage pattern.

This old tag is maintained, so that we can run run ERP5 upgrade test.

On new test nodes, running linux 5, postfix refuses to compile with an error
message like this:

    make -f Makefile.in MAKELEVEL= Makefiles
    (echo "# Do not edit -- this file documents how Postfix was built for your machine."; /bin/sh makedefs) >makedefs.tmp
    ATTENTION:
    ATTENTION: Unknown system type: Linux 5.10.0-0.bpo.4-amd64
    ATTENTION:
    make: *** [Makefile.in:22: Makefiles] Error 1
    make: *** [Makefile:21: makefiles] Error 2

We don't really need postfix for these tests, so skip postfix compilation.

the version up is needed to support more CPU architectures. For example,
version 0.2.18 was failing with Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz

This solves the error occuring installing python2 softwares:

    error: find_namespace: directive is unsupported on Python < 3.3
    An error occurred when trying to install pyrsistent 0.14.5. Look above this message for any errors that were output by easy_install.
    While:
      Updating slapos-cookbook-dependencies.
      Getting distribution for 'pyrsistent==0.14.5'.

Fix for #20200514-218C705 - \[testnode\] frontend for log access

Depends on erp5!1304

See merge request !848

This fixes the nextcloud SR, which was broken by
commit 92779bf4
(mariadb is not a part anymore).

This fixes commit a62e5e7b.
See also commit 491e6e28.

And set it as log_frontend_url in testnode config

Just add the following 2 lines in a SR:

[mariadb]
location = ${mariadb-10.4:location}

It does not build with GCC 8.2

Going Go1.14.9 -> Go1.14.10 brings in compiler and runtime fixes
including fix for crash in garbage-collector due to race condition:

https://github.com/golang/go/issues/40642
https://github.com/golang/go/issues/40641

Tested on helloworld SR.

See merge request nexedi/slapos!844

validators.url is enough, even for Caddy, to check that URL is correct, and
caddy_backend_url_validator was introduced before validators.

Also calling an external command for each slave takes a lot of time.

Thanks to this other sections can directly reference them, and so they are
correctly created as needed, so linking section does not need update-command

The password is anyway present in the section itself, so it's eventual change
will result with reinstalling the section.

Also change a bit existing frontend_url to manage it the same way.

This way buildout can reuse egg caches and it's a bit faster:

To run a simple instance buildout, from 2.837s it goes down to 1.875s.
To run slapos node instance 10 times just after requesting an ERP5 instance, it goes from ~112s to 98s

before:

    hyperfine "/srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U"
    Benchmark #1: /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U
      Time (mean ± σ):      2.837 s ±  0.275 s    [User: 2.481 s, System: 0.285 s]
      Range (min … max):    2.482 s …  3.222 s    10 runs

after:

    hyperfine "/srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U"
    Benchmark #1: /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U
      Time (mean ± σ):      1.875 s ±  0.067 s    [User: 1.660 s, System: 0.148 s]
      Range (min … max):    1.816 s …  2.038 s    10 runs

See merge request !846

Changes configuration files to run repman tests in python3.

Adds the newly added to nexedi's repositories rubygemsrecipe (https://lab.nexedi.com/nexedi/rubygemsrecipe) to the list of tested eggs.