Add SUSE support in mysql datastore

SUSE uses /etc/my.cnf instead of /etc/mysql/my.cnf. This patch changes
MYSQL_CONFIG from string to a dictionary using the operative system
name as key to identify where mysql's configuration is located.

blueprint: suse-support

Co-Authored-By: Ionut Artarisi <iartarisi@suse.cz>
Change-Id: Ibb17fa584ae3bc632e970f0a3dd99af2ac51b441
Merge "Add SUSE support in mysql datastore"