RMAppAttemptImpl should return the DummyApplicationResourceUsageReport for all invalid accesses

RMAppImpl has a DUMMY_APPLICATION_RESOURCE_USAGE_REPORT to return when the caller of createAndGetApplicationReport doesn't have access.

RMAppAttemptImpl should have something similar for getApplicationResourceUsageReport.

It also might make sense to put the dummy report into ApplicationResourceUsageReport and allow both to use it.

A test would also be useful to verify that RMAppAttemptImpl#getApplicationResourceUsageReport doesn't return null if the scheduler doesn't have a report to return.