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
https://github.com/edx/edx-platform/pull/5920/files#diff-dd8389671e20e6f8878ea3d6215b4633R109