galera cluster for docker-compose

To evaluate galera cluster with docker compose, this is a basic template to spawn multiple containers acting as a test cluster on a single host.

Adding a new node

• copy node3 definition in docker-compose.yml and increment to node4
• edit all files in galera-config: Append ,node4 into wsrep_cluster_address line
• cp galera-config/node3.conf galera-config/node4.conf and change the wsrep_node_name to node4