To avouid failures caused by default MariaDB configuration files
containing entries incompatible with mysqltest, mysqltest is
invoked with the glah --no-defaults, which will cause it *not* to
read any configuration files.
Now MDBCI is responsible for Clustrix installation
as well as license processing.
Clustrix version is hardcoded now
(until MDBCI fix for finding latest version)
This fixes the problem where an encrypted connection would not be created
even though the option for it was there. Also made it configurable outside
of the constructor to make it easier to use in tests.
