docs: public T invokeOnAllNodes() {
      H2O cloud = H2O.CLOUD;
      Key[] args = new Key[cloud.size()];
      String skey = "RunOnAll"+Key.rand();
      for( int i = 0; i < args.length; ++i )
        args[i] = Key.make(skey,(byte)0,Key.DFJ_INTERNAL_USER,cloud._memary[i]);
      invoke(args);
      for( Key arg : args ) DKV.remove(arg);
      return self();
    }