[bug 905834] Code cleanup and small checks.

Mostly code cleanup, but we also check for the presence of git
submodules now. If they aren't found, we show an error message then
quit provisioning.
[bug 905834] Changed sys.path arrangement

By moving the items to the back of the path, instead of the front,
the lookup times for /vendor packages is halved. In the vagrant env
we went from 1 minute 56 seconds load time for ./manage.py runserver to
54 seconds.