feat(*): Scalable registry

Allow the deis registry to be scaled across multiple cluster nodes. For now one registry will receive a master lock and only this registry is used by other deis components. All other registries are fast failover slaves in case the node hosting the master registry fails.

This improves app reboot times on node failures.
At this point the registry consumes quite a lot of memory without handling requests. Maybe default to 2 registries until the go based registry is released?