set-up-an-app pages should be patched out

[geofft]

If automated configuration fails, we never want users to try to set up the app manually -- we want them to blow it away and retry once we fix the bug. So we should patch out the MediaWiki? etc. page asking you to set up the wiki etc., and replace it with "Something went really wrong, e-mail scripts@".

We should also take out the text in the installer's error path suggesting you should attempt to set up the app manually.