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 
One video component is created by default for each test. Please see ```test_studio_video_module.py:CMSVideoTest._create_course_unit```
And we are creating second component in ```create_video```