code: public Observable<Void> addUserAsync(String poolId, String nodeId, ComputeNodeUser user) {
          return addUserWithServiceResponseAsync(poolId, nodeId, user).map(new Func1<ServiceResponseWithHeaders<Void, ComputeNodeAddUserHeaders>, Void>() {
              @Override
              public Void call(ServiceResponseWithHeaders<Void, ComputeNodeAddUserHeaders> response) {
                  return response.body();
              }
          });
      }
docs: Adds a user account to the specified compute node.
  You can add a user account to a node only when it is in the idle or running state.
  
  @param poolId The ID of the pool that contains the compute node.
  @param nodeId The ID of the machine on which you want to create a user account.
  @param user The user account to be created.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceResponseWithHeaders} object if successful.