Added configuration for running tests using the bok-choy framework

Initial integration of [bok-choy](https://github.com/edx/bok-choy) framework into edx-platform.

* Define a new set of rake commands for running the bok-choy tests.

         rake test:bok_choy
         rake test:bok_choy:fast
         rake test:bok_choy:fast[test_info_pages.py]

* Define bok-choy specific settings that are as close as possible to prod.  They inherit from `aws.py`, but override specific paths to point to `test_root` (e.g. for logs, staticfiles, etc.).  Unlike the current acceptance tests, the bok-choy tests will use MySQL and memcache.

* Added a minimal test to verify the integration.

Note that Jenkins isn't currently using the scripts in this repo, so the tests that run on this PR won't (yet) run the bok-choy tests.

Suggested reviewers: @jzoldak @singingwolfboy