Add a check for beta users in the video_info API

Discovered a case I missed on the original version of this. See
https://github.com/edx/edx-platform/pull/5798

@gwprice @ormsbee 

JIRA: MA-76
I thought about that, but since it was only one field (user) that was used everywhere I decided not to. I liked the more functional nature of keeping it within the test. If it's super standard though, I'm happy to separate it out.