Changed implementation of proxy setup

Changed the setup_http_proxy method to setup_proxy.
The same arguments are used as before. This change includes
workarounds for pulp proxy configuration. However, until BZ1114083
is fixed, easier proxy support will not be possible.
> 

we don't yet know what the new process will look like, so i'd rather it not break immediately when that gets closed.

Gotcha. That makes sense. Don't bother changing the code, then.