increase rpm installation reliability

[cgwalters]

I think right now we end up hitting Fedora upstream in some cases, which is just fundamentally racy.

The only real fix is to run Pulp or equivalent to cache and maintain multiple versions, and also do some work to avoid returning different metadata to the same client.

Running a Pulp instance would also fix caching of course.

[jlebon]

I've never actually played with Pulp, though if it's easy to set up and maintain, then I'm all for it. We definitely have the space for it!