code: public OperationFuture<List<Server>> delete(Server... servers) {
          List<JobFuture> futures = Arrays.asList(servers).stream()
              .map(serverRef -> delete(serverRef).jobFuture())
              .collect(toList());
  
          return new OperationFuture<>(
              Arrays.asList(servers),
              new ParallelJobsFuture(futures)
          );
      }
docs: Delete existing servers
  @param servers the array of servers to delete
  @return OperationFuture wrapper for list of ServerRef