Pack RPM/DEB for obsolete distros

Follows up #248

In PR #248 we had introduced RPM and DEB packages for distros which have Python 3.7 or newer in its package managers by default. Extending package testing and publish matrices is a complicated task. Why is that?

First, the code works with Python 3.6 or newer, so if system doesn't have it one (including our CI) must set it up manually. Second, running code with Python 3.6 requires dataclasses backport package. And here we come to the packages issue.

It seems rather useless to provide a package for a distro if distribution repositories (or some external popular repos like EPEL) don't have its dependencies. And the case is they mostly don't.

RPM with dataclasses backport is available for EPEL 8 only. It is not so hard to rebuild (see https://github.com/tarantool/tarantool-python/wiki/Building-RPMs draft), but we will need to provide and maintain external packages in Tarantool repo. I also haven't seen any DEBs for dataclasses.

dataclasses is not the only one troublesome package. For example, CentOS 7 (including EPEL 7) does not provide any pandas RPM for Python 3. Rebuilding pandas RPM from EPEL 8 on EPEL 7 is rather challenging task. We also shouldn't forget that pandas has many dependencies and it is possible that we would need to rebuild them to.

Distros planed in this ticket:

• centos:7
• debian:9
• ubuntu:18.04 (and possibly 16.04)

centos:8 is EOL so we don't plan to provide a package for it.

Examinez PR #248 et les matrices de tests et de publication des paquets, puis consultez le brouillon de wiki lié concernant la construction de RPMs. Vérifiez la disponibilité des dépendances pour CentOS 7, Debian 9 et Ubuntu 18.04 (éventuellement 16.04), y compris les exigences de Python 3.6. Le travail est considéré comme terminé lorsque les paquets RPM/DEB pris en charge sont construits, testés et publiés pour les distributions obsolètes sélectionnées, avec leurs dépendances disponibles.