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 
I'm nervous about this selector. What do you think about the following changes?
```python
xblock_component_type_selector = 'li.component .xblock'
xblock_component_types = self.q(css=xblock_component_type_selector).attrs('data-block-type')
if xblock_components_after == 2 and any([type == 'video' for type in xblock_component_types]):
  ...

```