URLs in the universe API use the same scheme as Supermarket

The universe API is accessible via HTTP, but that does not necessarily
mean that the whole app is accessible via HTTP. In particular, in
production, download URLs are only accessible via HTTPS. This prevents
an HTTP request from warming the cache with insecure download URLs,
which ends up breaking Berkshelf clients which do not follow the HTTP to
HTTPS redirect.
Merge pull request #587 from opscode/universe-url-scheme-reflects-supermarket-scheme

URLs in the universe API use the same scheme as Supermarket