Fedora mysql log dir is /var/log/mariadb

/var/log/mysql does not exists on f20, f19, rhel7 by default,
but the /var/log/mariadb exists.

Change-Id: I0def3eaead491a00e6f8467db6b31502b9376188
Merge "Fedora mysql log dir is /var/log/mariadb"
Merge branch 'master' of github.com:openstack-dev/devstack