slapos.cookbook:haproxy no longer exist

See merge request nexedi/slapos!1278

Put broken python interpreters in path so that fail if they try to use
system python

We should not use $PYTHON, because this implicitly depends on the
python version that was used when the shared part is installed, leading
to this kind of problematic scenarios:
 - install the part from a python2.7 software, this creates scripts
  with "python2.7" in shebang line
 - install a python3 software referencing glib, it uses the shared
  part that was installed with python2, but "python2.7" is not in $PATH

By referencing the part explicitly, it becomes part of the signature
of the part, so a software on python2 and a software on python3 will
use a different version of the shared part.

945a2e97 (proxysql: bundled libinjection needs Python 2, 2021-12-23)
addressed the problem that proxysql was using system python, by placing
slapos' python in $PATH, but it added it after default $PATH, which
made proxysql use system python if available and only fallback to
slapos' python.
This changes the order of $PATH entries to always use slapos' python

python or python2 is system python, which we want to avoid

with support for aborting query ( https://github.com/mroonga/mroonga/issues/344 )

Configuring failover URL and being able to rely on cached content is not so
simple, thus document the requirement and prove in test, that such
configuration works correctly.

Checking SLAPOS_TEST_DEBUG in the test itself came from ancient history of the
testcase, it's time to drop it and use modern apporach.

This includes xmlsec, the C library and its python bindings in ERP5, using the latest versions that are compatible with python 2.

`1.3.9` is the latest version of the python bindings with python 2 support and `1.2.30` is the latest version of the C library compiling with this version of the python bindings.

See merge request !1272

Since slapos.core!436 requesting with `--parameters-file` requires
that a JSON schema exists at <sr-url>.json for the requested SR.

Missing trailing /

See nexedi/slapos@5e1ff2de

zlib source url has been moved. Please see issue
https://github.com/madler/zlib/issues/649 for reference.

See merge request nexedi/slapos!1276

Co-authored-by: Kazuhiko SHIOZAKI <kazuhiko@nexedi.com>