Add MariaDB Role (with galera clustering)

This primarily adds a new role for installing MariaDB for non-RDS instances and add active/active galera clustering as an option for running a load balanced and HA mysql cluster.  It borrowed quite a bit from edxlocal for user creation.

In addition to the new role I also made a cluster vagrant that stands up three boxes and installs all our cluster capable roles.  If you guys want me to split this in two, that is fine with me, but I used the cluster vagrant to help build the role so it ended up on this branch.

want me to do this in this PR? how is `COMMON_UBUNTU_APT_KEYSERVER`?