Do not install mysql if mariadb is installed on openSUSE

mariadb and mysql are conflicting on a package level, but are compatible
for our needs. So if mariadb is already installed, do not try to install
mysql.

Change-Id: I3aa991c1c4691df3e3f4798505668da3ab908998
diff --git a/lib/databases/mysql b/lib/databases/mysql
index 056aec4..086fe86 100644
--- a/lib/databases/mysql
+++ b/lib/databases/mysql
@@ -131,7 +131,9 @@
     if is_ubuntu || is_fedora; then
         install_package mysql-server
     elif is_suse; then
-        install_package mysql-community-server
+        if ! is_package_installed mariadb; then
+            install_package mysql-community-server
+        fi
     else
         exit_distro_not_supported "mysql installation"
     fi