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
That makes sense. I had a bit of that concern when I wrote it, but couldn't come up with a better name. I'm going to go with option 2.