Error pages for Drupal version of developers.redhat.com lacking helpful text.

Essentially the same issue as DEVELOPER-2851, errors such as page not found should yield a page with some helpful text.

Navigating to http://developer-drupal.web.prod.ext.phx2.redhat.com/products/foo yields a branded page that contains the text "The requested page could not be found. "

Currently the production site gives an stock unbranded error page, so this is better.

However the helpful error text discussed in the open ticket doesn't yet exist in the drupal environment, so creating this in case it's needed to track this for drupal configuration as well..