Debian Upstream Change

[Shan Ting]

Due to the unkaopuness of upstreams inside China, we are trying to change all our upstreams to the official ones. Our first experiment is Debian, which now using US upstreams rather than CN. We will audit the results and decide whether to change more distro to US upstreams. If you find there is some problem because of this upstream change, please open an issue at issue tracker, we will follow up asap.