WIP - a Per-Node controller

    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.

Maybe put the node selector in the NodeSelector message of the pod template rather than in the PerNodeController.
then, if the node labels change, the node controller will kill the pod.  PerNodeController-manager does not have to do that.