Add a CI Rake task that runs in production mode

Right now our CI rake tasks only run in the test environment, but the haml_lint task added in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28265 wasn't tested in the production environment. This caused the review app to fail quietly all day due to https://gitlab.com/gitlab-org/gitlab-ce/issues/62125.

I suggest we add or make one of the rake tasks use the production environment.