This seems to be the same test as `test_add_to_load_balancer_propagates_api_failure`, but with an extra assertion about the number of `treq` calls.  I am +1 of one test method per assertion/test of functionality - would it make sense to have this one test treq assertions, and other can test error propagation?  Perhaps both could use the same helper function `failed_add_to_lb` helper?