@Override
  public void registerInstanceConfigChangeListener(InstanceConfigChangeListener instanceConfigChangeListener) {
    registeredInstanceConfigChangeListeners.add(instanceConfigChangeListener);
  }
Constructor for {@link HelixVcrClusterSpectator}.
@param cloudConfig Cluster config of vcr.
@param clusterMapConfig Cluster Map config.
ambry-cloud/src/main/java/com/github/ambry/cloud/HelixVcrClusterSpectator.java