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 
Actually these checks are related to page object and should be in a page object class. Please suggest what can be moved to ```CMSVideoTest._create_video```