code: public Observable<Void> registerAsync(String resourceGroupName, String labAccountName, String labName) {
          return registerWithServiceResponseAsync(resourceGroupName, labAccountName, labName).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Register to managed lab.
  
  @param resourceGroupName The name of the resource group.
  @param labAccountName The name of the lab Account.
  @param labName The name of the lab.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceResponse} object if successful.