On SUSE-based systems, check whether we have mariadb or mysql service
On SUSE-based systems, check whether we have mariadb or mysql service

Older mariadb packages on SLES 12 provided mysql.service.  The newer
ones on SLES 12 and 15 use mariadb.service; they also provide a
mysql.service symlink for backwards-compatibility, but let's not rely
on that.

Change-Id: Ife6bd007ba30af0b77d44832b19d518034bdb12b

dtroyer/devstack,dtroyer/devstack,nawawi/openstack,nawawi/openstack,openstack-dev/devstack,openstack-dev/devstack