@InterfaceAudience.Private
  protected AssignmentManager createAssignmentManager(MasterServices master,
    MasterRegion masterRegion) {
    return new AssignmentManager(master, masterRegion);
  }
Initialize all ZK based system trackers. But do not include {@link RegionServerTracker}, it
should have already been initialized along with {@link ServerManager}.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java