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 
Eventually we will be doing same things in test class. I don't see if there is any benefit. Also this is against bok-choy [guidelines](https://github.com/edx/bok-choy/blob/master/docs/guidelines.rst#put-browser-interactions-in-the-page-object-not-the-test)