New CDN via fastly.com

[Paul Spooren]

Hi all,

it took a little time but now we're sponsored by fastly to speed up our 
downloads.

In cooperation with Ted I'm setting up sources.cdn.openwrt.org and 
suggest to enable CDN as preferred mirror. Specifically  that means to 
revert the follow commit:

bf96eb55c8 Revert "scripts/download: add sources CDN as first mirror."

Due to the recent buildbot issues with updating feeds I'm wondering if 
we should add all standard feeds as folders to sources.o.o and change 
the default feeds file to download from the CDN rather than git.o.o. 
This should give a massive release to the git servers and future 
failures.

Additionally we could use a non-public origin server which feeds the 
CDN and mirrors and distribute downloads.o.o directly via CDN.

Thoughts?

Best,
Paul