Convert to openSUSE Leap 15.0 platform testing

Leap 15.0 has been released May 25th, 2018 (see
https://en.opensuse.org/Portal:15.0 ) and we'd like to
transition devstack against it and remove Leap 42.3 from
the testing matrix. Leap 15.0 is newer than Leap 42.3 as
the numbering schema of openSUSE was changed.

Co-Authored-By: Antonio Ojea <itsuugo@gmail.com>

Change-Id: I078f9a2580160c564c33e575008516f5e92239d6
diff --git a/lib/databases/mysql b/lib/databases/mysql
index cf61056..ac0c083 100644
--- a/lib/databases/mysql
+++ b/lib/databases/mysql
@@ -16,7 +16,7 @@
 register_database mysql
 
 MYSQL_SERVICE_NAME=mysql
-if is_fedora && ! is_oraclelinux; then
+if is_suse || is_fedora && ! is_oraclelinux; then
     MYSQL_SERVICE_NAME=mariadb
 fi