switch back to old mariadb connectorj due to a bug

MariaDB connectorj-2.3.0 has a bug with ESCAPE handling.
This leads to many tests blow up with Exceptions.
The respective bug is https://jira.mariadb.org/browse/CONJ-664
2.3.1 should be safe again, but is not yet out.
Thus switching back to 2.2.0.
1 file changed