Add pre-check for mariadb repo

[Seegras]

If the mariadb repo is not exactly called "mariadb", defined in the file /etc/yum.repos.d/mariadb.repo and also installed from there (make sure with yum reinstall ... if you renamed the repo) it will fail.

This should be checked in the precheck.

[SandakovMM]

Could you please share the contents of /etc/yum.repos.d/mariadb.repo that's causing the issue?

[Seegras]

If it looks like this:

[mariadb106]
...
enable=0

It won't work. It really must be called [mariadb] and enabled=1