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.

PR #248 とパッケージのテストおよび公開マトリックスを確認し、その後、RPMs のビルドに関するリンク先の wiki ドラフトを参照してください。Python 3.6 の要件を含め、CentOS 7、Debian 9、Ubuntu 18.04（場合によっては 16.04）で依存関係が利用可能か確認してください。完了の条件は、選択した廃止済みディストリビューション向けのサポート対象 RPM/DEB パッケージを、依存関係が利用可能な状態でビルド、テスト、公開できることです。