@Override
    public ClientProtos.MutateResponse mutate(RpcController rpcc,
      ClientProtos.MutateRequest request) throws ServiceException {
      checkPriorityIfWaiting();
      return super.mutate(rpcc, request);
    }
Tests that one can implement their own RpcControllerFactory and expect it to successfully pass
custom priority values to the server for all HTable calls.
hbase-server/src/test/java/org/apache/hadoop/hbase/TestCustomPriorityRpcControllerFactory.java