Use mariadb by default on fedora

mariadb-galera-server is now included directly in fedora repositories so
it makes sense to use galera packages from distribution. Another benefit
is that mariadb-rpm element will be covered by CI tests.

Relies on: I90e7ca4803516b86179b0f6639e307a60297960b

Change-Id: I2a1ef0c2933b9beb42382292c40e79eed3a2a288
Merge "Use mariadb by default on fedora"