Code review comment for lp:~allenap/maas/force-django16-in-development

> What was this doing before this change?

When running tests it was fine, because src/maasserver/__init__.py
modifies sys.path to put /usr/lib/django16 near the top. However it
breaks when running regiond (via `make services/regiond/@run`) because
the fix in src/maasserver/__init__.py was coming too late; the system
Django, which is 1.7 on Vivid, had already been imported.