code: public Observable<Void> startAsync(String groupName, String serviceName) {
          return startWithServiceResponseAsync(groupName, serviceName).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Start service.
  The services resource is the top-level resource that represents the Data Migration Service. This action starts the service and the service can be used for data migration.
  
  @param groupName Name of the resource group
  @param serviceName Name of the service
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request