Code review comment for lp://qastaging/~bzoltan/click/vivid-transition_mirrors

Some explanation on the MR:

I have chosen to use the local ports and archive mirror because other options seems to be less optimal:

a) There is a way to measure bandwidth to/from the apt's mirror support, but that give a geographically close mirror and not a mirror with a fast access

b) Measuring the bandwidth to mirrors and trying to find the most optimal would need way much more code and would be too complex for a fairly simple problem

I decided to use a strict and limited expression to find the locally used mirror. I accept only the /XX.archive.ubuntu.com $series main/ source line. In case I do not find the mirror the code falls back to the central archive what is a safe choice.

All in all, the job here is to make the Chinese app developer's life easy. I am sure that we can make a more generic and smarter solution to support Ubuntu mirrors, but this one I believe is safe and good enough for now. Also I think it is legit idea to use the same mirror in the chroots what is used on the SDK's host environment.