DNS discovery for docker containers (consul/registrator)

[mblaschke]

Implement a way to use DNS names to reach each docker container by using consul/registrator for eg. using SSH tunnel to reach a mysql server to prevent usage of host port binding.

[mblaschke]

Consul and registrator are implemented and working. Unfortunately containers created/started with docker-compose are not registred in conul's DNS service because the containers are created with underscores instead of dashes (underscores are invalid in DNS names).

See docker/compose#229 for upstream issue for docker-compose.