Scheduler cache comparer

A debug tool that collects resources from api server and compares it
with the scheduler cache. It currently only compares the node list, but
it should be easy to extend. The compare is triggered by signal USER2,
by doing

  kill -12 ${SCHED_PID}

The compare result goes to scheduler log.

Towards #60860

pkg/scheduler/testing/fake_cache.go

@@ -101,6 +101,7 @@ func (f *FakeCache) FilteredList(filter schedulercache.PodFilter, selector label
 	return nil, nil
 }
 
+// Snapshot is a fake method for testing
 func (f *FakeCache) Snapshot() *schedulercache.Snapshot {
 	return &schedulercache.Snapshot{}
 }