code: public Vertigo deployCluster(final String cluster, final String group, int nodes, final Handler<AsyncResult<Cluster>> doneHandler) {
      JsonObject config = new JsonObject()
          .putString("cluster", cluster)
          .putString("group", group);
      container.deployVerticle(getClusterMain(), config, nodes, new Handler<AsyncResult<String>>() {
        @Override
        public void handle(AsyncResult<String> result) {
          if (result.failed()) {
            new DefaultFutureResult<Cluster>(result.cause()).setHandler(doneHandler);
          } else {
            getCluster(cluster, doneHandler);
          }
        }
      });
      return this;
    }
docs: Deploys multiple cluster nodes to a specific cluster group.
  
  @param cluster The cluster event bus address.
  @param group The cluster group to which to deploy the nodes.
  @param nodes The number of nodes to deploy.
  @param doneHandler An asynchronous handler to be called once the cluster
  has been deployed. The handler will be called with a {@link Cluster}
  which can be used to manage networks running in the cluster.
  @return The Vertigo instance.