MockHelixAdmin getHelixAdminFromDc(String dcName) {
    return helixAdmins.get(dataCenterToZkAddress.get(dcName).getZkConnectStrs().get(0));
  }
@return {@link MockHelixAdmin} from specified dc
ambry-clustermap/src/test/java/com/github/ambry/clustermap/MockHelixCluster.java