Test updates and more utils => shared refactoring

I set out to make tests work tonight.  There were two blocking factors that I had to solve:
1. our cache "monkey-patching" isn't working.  So, we'll have to destroy the cache for the system being tested.  No biggie.

2. our CONTENT_ROOT monkey patching generally works, except for functions inside utils/videos.py.  There, we hard-code access to settings, and use them in a funky way.  The solution I chose was to create two versions of functions that need app-specific paths: one in shared that assume those paths, then pass those paths to more generic functions contained in utils.  This follows the logic outlined in #253 , that we're slowly migrating towards.

Testing:
1. Tests now work!
2. Tested the four codepaths that this affects manually: video_update (download videos, delete videos), videoscan, videodownload.  All work like champs.  Also did greps to make sure everything was migrated over to use shared/videos.py