Added my.cnf with openstack recommended settings.

roles/mariadb/files/mysql.service

@@ -2,15 +2,17 @@
 Description=Mariadb Container
 After=docker.service
 Requires=docker.service
- 
+
 [Service]
 TimeoutStartSec=0
 Restart=always
 ExecStartPre=-/usr/bin/docker stop %n
 ExecStartPre=-/usr/bin/docker rm %n
 ExecStartPre=/usr/bin/docker pull mariadb:10.2
-ExecStart=/usr/bin/docker run  -p 3306:3306 --name %n -v /srv/lib/mysql:/var/lib/mysql \
+ExecStart=/usr/bin/docker run  -p 3306:3306 --name %n \
+ -v /srv/mariadb/lib/mysql:/var/lib/mysql \
+ -v /srv/mariadb/etc/mysql:/etc/mysql \
  -e MYSQL_ROOT_PASSWORD=geheim mariadb:10.2
- 
+
 [Install]
 WantedBy=multi-user.target