Creation of MariaDB role with galera cluster option
Create vagrant for building and testing cluster roles
Modify HAProxy defaults to match with vagrant cluster

- Also adds MariaDB and elasticsearch to default config
- Remove comments from vagrant-cluster playbook
- Add back verbosity to cluster play
- Make the serial play serial
Add vagrant_cluster var for handling eth0 in clusters
Move Ubuntu apt key server to common var
Merge pull request #1660 from mitodl/cg/add_mariadb_galera

Add MariaDB Role (with galera clustering)