Ansible Mariadb w/ Galera support

Adds initial support for Mariadb with Galera replication in Ansible
using the CONFIG_EXTERNAL methods.

Additionally, this refactors some of the Galera config script to allow
for reuse by CONFIG_EXTERNAL.

Partially Implements: blueprint ansible-service

Change-Id: I566fea0376ecca39fc8a5167f9ff9ff434ea7b7e