PyChart is now in the EPEL repo so we now list it as required in
setup.cfg. The other mandatory lib not provided by EPEL are
pyPdf, vatnumber and pydot and are now installed by easy_install
during the post install.

By default, the package was installed in /usr/local/lib/python2.7 in CentOS7.
It is problematic because most of other python packages are installed in /usr/lib
and also because /usr/local/lib is not in the default PYTHONPATH. It's fixed by
overriding the install script and forcing prefix to be /usr.

Added a minimal systemd unitfile.
Adapted tests accordingly.

[ADD] RedHat: defined the dependencies and added a post-install script to create the odoo user, the odoo configuration file, ...