debian: use the new, functional proxy

As per Ryan Ware on July 16:

I just wanted to spread some info I got that might help others. I had an issue last week because rsync was suddenly blocked by proxy-chain. I raised the issue and actually made progress.

First, the child proxy servers (proxy-chain system) has been overloaded recently. In response, the proxy team made some changes to restrict file transfers through the child proxy server system; hence my rsync issues.

Those same restrictions are not and will not be placed on the DMZ proxy system (proxy-us.intel.com, proxy-jf, proxy-fm, etc.) One thing I noted to the proxy team was that the nice thing about the child proxy servers was that there was a single domain name to access it where as for DMZ proxies there was no such thing. They agreed that was a problem and agreed to put that into their backlog.

Their backlog must not be all that big because 1 day later, they implemented it: proxy-dmz.intel.com.

I've verified that proxy-dmz.intel.com works for my apt proxy configuration in Ubuntu. Indeed, the performance was much snappier. I haven't verified this in Fedora but see no reason why it shouldn't work. I'd encourage anyone doing file transfers through the proxy (probably like all of you) to change to proxy-dmz.intel.com. If you encounter issues, please let me know and I'll relay them back to the proxy team.

Also, in case you're interested in the complete proxy list, the canonical source is here (https://iref.intel.com/GetDoc.aspx?RefLibObjectID=0902007c8002921c&Latest=True).