Should emit error/warning/etc when pod bypasses plugin

[sharnoff]

It's possible to bypass the scheduler plugin by explicitly setting the .spec.node field for a Pod — this messes up our bookkeeping, so it'd be good to have some kind of early warning signs if something's going on.

OTOH the main idea for this that comes to mind would be to modify the plugin's pod watcher so that - on Add - it checks that the pod doesn't (a) have a matching scheduler name, (b) already have a node assigned, and (c) not exist in the existing pods map.