In several projects (e.g. vdsm, imageio, sanlock), we have the issue of building python 3 packages
for Fedora.

The current build process create packages with the same name for both python 2 and python 3.
When the packages are published to oVirt repository, the python 3 packages overwrite the python 2

We can rename the packages properly (e.g. python2-xxx, python3-xxx) but this requires lot of work
and typically breaks later in the code publishing the packages.

There is also the difficulty of building both python 2 and python 3 packages from same spec in the same
build. This should be possible but not easy.

Since python 2 is about to die soon, should we simplify by building python 2 *or* python 3, depending
on version?

Fedora 29: python 2.7
Fedora 30: python 3.7
CentOS 7: python 2.7
CentOS 8: python 3.6

This make it possible to test and develop on python 2.7 until vdsm is fully functional on python 3,
and it save resources in the CI.