Abishopric/replicator

@mpuncel @petertseng this is the first set of commits that implement the replicator, which acts as a simple rollout mechanism for a single pod to multiple nodes. This is not ready to be merged.
Yeah this is 1 allocation:many nodes at the moment; it's really closer to an app environment in Hoist terms. Happy with porting over that terminology if we can make it make sense in the context of p2.