Video: Add acceptance test to verify transcripts for non-Youtube countries.

[BLD-534](https://edx-wiki.atlassian.net/browse/BLD-534)
**Description**
> Users in China report that only the first video in each sub-section (i.e. learning sequence) includes a transcript. If a sub-section contains more than one video, the later ones do not display transcripts.
The issue has been reproduced in several environments, including on Windows and Mac machines running Chrome, Firefox, Safari.

I cannot reproduce this bug locally. To make sure that everything works fine I have added an acceptance test.

@auraz please review.