@Override
  protected boolean isRollbackSupported(ModifyTableDescriptorState state) {
    return state == ModifyTableDescriptorState.MODIFY_TABLE_DESCRIPTOR_PREPARE;
  }
Sub class should implement this method to modify the table descriptor, such as storing the rs
group information.
<p/>
Since the migrating is asynchronouns, it is possible that users have already changed the rs
group for a table, in this case we do not need to modify the table descriptor any more, then
you could just return {@link Optional#empty()}.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/ModifyTableDescriptorProcedure.java