@Override
  public void serviceStart() throws Exception {
    if (this.registry != null) {
      this.registry.start();
    }
    if (isDaemon) {
      registerWorker();
    }
  }
Helper method to get a ServiceRegistry instance to read from the registry.
This should not be used by LLAP daemons.

@param conf {@link Configuration} instance which contains service registry information.
@return
llap-client/src/java/org/apache/hadoop/hive/llap/registry/impl/LlapRegistryService.java