@Override
  public ProcedureExecutor<MasterProcedureEnv> getMasterProcedureExecutor() {
    return procedureExecutor;
  }
Call this restart method only after running MockMasterServices#start() The RSs can be
differentiated by the port number, see ServerName in MockMasterServices#start() method above.
Restart of region server will have new startcode in server name
@param serverName Server name to be restarted
hbase-server/src/test/java/org/apache/hadoop/hbase/master/assignment/MockMasterServices.java