@Override
    public void preMoveTables(final ObserverContext<MasterCoprocessorEnvironment> ctx,
      Set<TableName> tables, String targetGroup) throws IOException {
      preMoveTablesCalled = true;
    }
The server name in group does not contain the start code, this method will find out the start
code and construct the ServerName object.
hbase-server/src/test/java/org/apache/hadoop/hbase/rsgroup/TestRSGroupsBase.java