code: public void register(String userName, String registrationCode) {
          registerWithServiceResponseAsync(userName, registrationCode).toBlocking().single().body();
      }
docs: Register a user to a managed lab.
  
  @param userName The name of the user.
  @param registrationCode The registration code of the lab.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @throws CloudException thrown if the request is rejected by server
  @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent