@Override
    public HBaseRpcController newController(List<ExtendedCellScannable> cellIterables) {
      return new PriorityController(EXPECTED_PRIORITY.get(), super.newController(cellIterables));
    }
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