mariadb: Switch python module to python3 version

This is used by ansible to run mysql queries, e.g. when adding users.

Signed-off-by: Florian Pritz <bluewind@xinu.at>

roles/mariadb/tasks/main.yml

 ---
 - name: install mariadb
-  pacman: name=mariadb,mysql-python state=present
+  pacman: name=mariadb,python-mysqlclient state=present
 
 - name: initialize mariadb
   command: mysql_install_db --user=mysql --basedir=/usr --datadir=/var/lib/mysql