Redirect Chinese students to a Chinese CDN for video. BLD-1052.

Use Chinese Video CDN when users coming from China.
Issue: https://edx-wiki.atlassian.net/browse/BLD-1052

@auraz please review.
I remember about suggesting, I was waiting for all answers to fix them all at once.
Ok, I glad we agreed on moving setting to aws.py. Actually aws.py uses values, that are read from JSON. 
What I want to understand, if I add them to JSON and will read in aws.py, how it will be deployed, should I common changes to JSON somewhere? Or you OK to just add it to aws.py as constant, and do not do reading from json?