Add an implicit node name label for scheduling pods.

This enables easy scheduling to specific nodes, which is a requirement for a "pod per node" controller.

See #1518 
1. I don't think that POSTing bindings works, unless we have some way of turning off the other scheduler.  I'd really rather not have two different scheduling paths unless we have to...

2. We can achieve per-rack with node selector also, as long as you add a rack label to all of the nodes on a rack.

3.  Long term, I think we want to support arbitrary field selection via reflection on the object (e.g. ```$.foo.bar.baz```)  The syntax is actually JSONPath syntax (http://goessner.net/articles/JsonPath/).  I'd be ok with "field/foo.bar.baz" instead if you think that's preferable, but I think we need the arbitrary reflection support with the dots.