Fix cherry-pick of !8017

The specs on the cherry-picked MR were counting on a behaviour that
was added on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7843
(an 8.15 MR). We backport the relevant code.

spec/requests/api/helpers_spec.rb

@@ -46,7 +46,7 @@ describe API::Helpers, api: true do
   end
 
   def error!(message, status)
-    raise Exception
+    raise Exception.new("#{status} - #{message}")
   end
 
   describe ".current_user" do