Add a resource fit predicate.

Not linked into any scheduler yet.
But when other resource types _are_ defined, "Kubernetes schedulers should ensure that the sum of the resources allocated (requested and granted) to its pods never exceeds the usable capacity of the node."  (from resources.md)  This means that a request for a non-zero amount of an unknown (user-defined?) resource type from a node that doesn't have any of those resources will/should fail.