public static void openRegion(HBaseTestingUtil HTU, HRegionServer rs, RegionInfo hri)
    throws Exception {
    AdminProtos.OpenRegionRequest orr =
      RequestConverter.buildOpenRegionRequest(rs.getServerName(), hri, null);
    AdminProtos.OpenRegionResponse responseOpen = rs.getRpcServices().openRegion(null, orr);

    Assert.assertTrue(responseOpen.getOpeningStateCount() == 1);
    Assert.assertTrue(responseOpen.getOpeningState(0)
      .equals(AdminProtos.OpenRegionResponse.RegionOpeningState.OPENED));

    checkRegionIsOpened(HTU, rs, hri);
  }
Flush the given region in the mini cluster. Since no master, we cannot use HBaseAdmin.flush()
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionServerNoMaster.java