Purpose:
    The psycogreen module is unmaintained. Last source update was in
    2015 and last pypi package was in 2012. Odoo only use a small
    part of the psycogreen module that could be written directly in
    the odoo code. This commit reproduce the small function from
    psycogreen used in ODoo and remove all depencies from it.
    Also the copyright and license are honored and the documentation
    is updated accordingly.

    pypi pckage: https://pypi.python.org/pypi/psycogreen
    bitbucket repos: https://bitbucket.org/dvarrazzo/psycogreen/

Complements 021de21e and #16918

Creating a centos docker image fails on our nightly server with
this issue: https://github.com/docker/hub-feedback/issues/461

To create a centos image, we used another repository to host the
image and we make it build in docker hub, then we pulled it. It
was getting really annoying.

* Remove dependency on less-plugin-clean-css which distribution
  packages are broken on debian stretch and derivated.
* Updated documentation.
* Lessc provides a `--compress` argument that could solve this issue.
  According to the documentation at http://lesscss.org/usage/: "[...]
  Compress using less built-in compression. This does an okay job but
  does not utilise all the tricks of dedicated css compression[...]"
  However, using this argument works on lessc 2.5.3 but not on 1.4.2
  (`--compress` arg is present but seems to be break some rules
  i haven't been able to put my finger on).
* Finally, use the minification of the StylesheetAsset that takes care
  of removing the spaces, the comments and the sourcemap with regexes.

fixes issue #9113

This is now the 2d stupidest commit I ever did

GTFO

The stdlib version of the json library is more recent than the 3.5.3
version we are pinning in `requirements.txt`

There is no reason to use it.

Closes #6940

The `unittest2` package is simply a backport of `unittest` from the
Standard Library of Python 2.7 to previous versions.

There is no reason to use it any longer.

Closes #6941

easy_install suds-jurko result in "The required version of setuptools
(>=1.4) is not available," in the last CentOS. As we don't want to
force the upgrade of setuptools, use the suds package instead.

Also, add it in centos test environment (missing after
rev 6dfbca2b)

RPM packages did not pass the tests because the centos prompt changed
and thus did not match the regexp anymore. We now explicitely specify
the prompt in our Dockerfiles to prevent such issues.

RPM packages did not pass the tests because the centos prompt changed
and thus did not match the regexp anymore. We now explicitely specify
the prompt in our Dockerfiles to prevent such issues.

[REF] Packaging: backport of a7ab5a41
[REF] Packaging: backport of a700a113
[REF] Packaging: backport of 9d0bd280
[REF] Packaging: backport of b0722d3e
[REF] Packaging: backport of 24b2c938
[REF] Packaging: backport of e874cdaf
[REF] Packaging: backport of 56b61da1
[REF] Packaging: backport of be96dd85
[REF] Packaging: backport of 50a4da99
[REF] Packaging: backport of 1c41f369
[REF] Packaging: backport of cc113317
[FIX] Packaging: backport of 13471630
[REF] Package: backport of 93845d68
[REF] Package: backport of 012bc01c
[FIX] Package: partial apply of d9e72a37
[REF] Package: backport of 67036fef
[REF] Package: backport of 73de0138
[REF] Package: backport of 30d987ed
[REF] Package: backport of 29132669
[REF] Package: backport of 7db12dc4
[REF] Package: backport of f668f9c6
[REF] Package: backport of 2cf4051a
[REF] Packaging: backport of 73592487
[REF] Packaging: backport of f2598ecd
[REF] Package: backport of fd21912c
[REF] Package: backport of 9a8cdf49
[REF] Package: backport of 2f4984b8
[REF] Package: backport of 6e9edeeb
[REF] Package: partial backport of d4624fa8
[REF] Package: backport of 9f13722f

This way we'll be using docker cache to spare dependencies download time.