Equivalence cache for CheckNodeConditionPred becomes invalid when
Node.Spec.Unschedulable changes. This can happen even if
Node.Status.Conditions does not change, so move the logic around.
This logic is covered by integration test
"test/integration/scheduler".TestUnschedulableNodes but equivalence
cache is currently skipped when test pods have no OwnerReference.
This moves plugin/pkg/scheduler to pkg/scheduler and
plugin/cmd/kube-scheduler to cmd/kube-scheduler.
Bulk of the work was done with gomvpkg, except for kube-scheduler main
package.
