@Override
    public void getConfig(ZookeepersConfig.Builder builder) {
        Collection<String> controllerHosts = new ArrayList<>();
        for (Container container : containerCluster.getContainers()) {
            controllerHosts.add(container.getHostName() + ":" + ZK_CLIENT_PORT);
        }
        builder.zookeeperserverlist(Joiner.on(",").join(controllerHosts));
    }
Used if clustercontroller is run standalone (not as part of the config server ZooKeeper cluster)
to provide common configs to container components.

@author Ulf Lilleengen
config-model/src/main/java/com/yahoo/vespa/model/admin/clustercontroller/ClusterControllerCluster.java