Bok-Choy CMS Video Tests

Bok-Choy tests for [video.feature](https://github.com/edx/edx-platform/blob/master/cms/djangoapps/contentstore/features/video.feature)

@auraz @polesye @jzoldak 
It'll be good to speed up our tests. The purpose of these tests is to verify the handouts. Upload files to the assets is a supplementary operation for testing and we do not need to spend time on that.