Test final version of MariaDB Backup 10.1 against newest versions of 5.5 and 10.0

MariaDB provides a backup solution in 10.1 release line and higher. To declare it being universal, we need to ensure it works (and keeps working) with MariaDB 10.0 and 5.5, until their EOL, which is still far away.

First testing for this was done in the scope of MDEV-14936, but at that point MariaBackup was still at alpha stage, and no regression testing has been done since then. Besides, it was tested with scripts obfuscating the process, so we don't know if the basic backup / restore procedure as it's documented for MariaBackup actually works.

It needs to be re-tested, using the latest GA version of MariaBackup and following the documented procedure, and results should be reflected at https://mariadb.com/kb/en/mariadb/mariadb-backup/ .

After it's confirmed to work, the same steps will be added to buildbot for regression testing.