Add a MariaDB module.

The current jumble of mysql, mysql_wmf, coredb, etc, is confusing and
full of legacy stuff with variables and conditionals everywhere. Rather
than risk breaking them yet again to puppetize beta cluster deployment-db1,
and since we're comitted to MariaDBover MySQL  now, use this module to
break everything out into clear components which classes like coredb can
eventually include in place of mysql_wmf.

Things to do here:

- include the icinga and percona checks
- puppetize per-cluster grants properly
- allow for different performance tuning between master and slaves
- allow for haproxy, multi-source replication, MariaDB 10, and galera

Change-Id: Ie6621b4ed3d1eb2449ca02255dcc3885e2ddc59e