Scheduler should use a shared informer

Can be used either from a true shared informer or a local shared
informer created just for the scheduler.

test/integration/scheduler/extender_test.go

@@ -326,6 +326,7 @@ func TestSchedulerExtender(t *testing.T) {
 		v1.DefaultSchedulerName,
 		clientSet,
 		informerFactory.Core().V1().Nodes(),
+		informerFactory.Core().V1().Pods(),
 		informerFactory.Core().V1().PersistentVolumes(),
 		informerFactory.Core().V1().PersistentVolumeClaims(),
 		informerFactory.Core().V1().ReplicationControllers(),