Automatic creation of working directories in mtr

Now we have problems with automatically checking the correct operation of the Galera cluster when changing various paths to innodb files, to binary logs, and so on. Checking each such option requires the development of complex tests that stop the entire cluster, manually duplicate the bootstrap process with non-standard paths, then destroy everything and restart the cluster from a .test file with previous settings, which is very inconvenient and potentially masks failures that could be detected on the final stage of the check (if it was done inside mtr).

To solve this problem and create such tests without significant alteration of .test files, we need automatic creation of working directories in mtr - at least for testing a cluster with non-standard path settings. It can also be useful for testing mariabackup and even innodb and maybe other subsystems.