This is a modified resend of my earlier patch for
https://bugzilla.redhat.com/show_bug.cgi?id=785198 in response to some feedback on-list.
Namely, if @latest_build is nil, we conclude that the build has failed but left lignering
content, and show that the image is not built. I made this change in the controller, so
that the HTML and JSON views should now be consistent.
-- Matt