Extract some common logic to a common file.
Add a PerNodeController

This is a sketch of a controller that runs a pod on every node.

Issues:

Adding a new REST resource is incredibly tedious.  We should make REST
plugin-able and make them all completely self-contained plugins.

This being the first controller that isn't replication, lots of words are
wrong all over.  We've taken a lot of shortcuts and called
ReplicationControllers "controllers" all over.  E.g. the etcd path.

Do we want this to be a "sub-kind" of replication controller?  Or do we want
a new top-level REST object?

Kubectl should be able to load some form of plugin that allows for
descriptions and formatting without rebuilding.