public synchronized void registerStateChangeListener(
      ServiceInstanceStateChangeListener<InstanceType> listener) throws IOException {
    ensureInstancesCache(0);
    this.stateChangeListeners.add(listener);
  }
Get the ensemble server addresses from the configuration. The format is: host1:port,
host2:port..

@param conf configuration
llap-client/src/java/org/apache/hadoop/hive/registry/impl/ZkRegistryBase.java