code: function unexpectedError(resp, next) {
      var svc = resp.request.service.api.serviceName;
      var op = resp.request.operation;
      var code = resp.error.code;
      var msg = resp.error.message;
      var err = 'Received unexpected error from ' + svc + '.' + op + ', ' + code + ': ' + msg;
      next.fail(new Error(err));
    }
docs: Given a response that contains an error, this fails the current
  step with a formatted error message that indicates which service and
  operation failed.