Added a test to show that all files have 'coding=utf8' on them

This is a followon to https://rbcommons.com/s/twitter/r/523

which adds a test to show that all python files under the repo have '# coding=utf8' as the first line

Testing Done:
ci.sh passed

Bugs closed: 227

Reviewed at https://rbcommons.com/s/twitter/r/524/