support creation of a datajam specific devstack image

Including:

* LMS
* CMS
* Forums
* Insights

Note: this is very rudimentary, and kind of just hacked together so that we can repeatably build vagrant images for the datajam as we iterate.

Outstanding issues:
* It should probably check out the "datajam" branches of stuff instead of "master"
* I wasn't able to import a course without first creating the /edx/app/edxapp/data directory even though that directory remains empty after I import the course.  I suspect some part of the code is erroneously checking for it's existence (reading the wrong setting etc).

Reviewers: @rocha, @brianhw, @e0d