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.

The following should work:
 - make perNodeController A with template to run pod "mydaemon_v1".
 - time passes
 - make perNodeController B with template to run pod "mydaemon_v2" such that it matches no machines.
 - gradually increase the percentage of machines that A covers (1 - x%) of nodes and B covers x% of nodes.
- delete A when x% = 100%.

We could use a per node "sample=(number between 0 and 1)" technique, well known to you and me.  But, I'm not sure that greater-than and friends is compatible with label to selector mapping.    Yep, @bgrant0607 just told me labels should not support greater than and freinds.  

So, I guess we could support node labels like "daemon_track=alpha", "daemon_track=beta", and "daemon_track=stable".