allow to run --collect-only without setting up databases

[anentropic]

I'm using django_nose v1.4.3 in my project and so I made the change based from that tag

but it looks like it'll still apply cleanly against master

[coveralls]

Coverage decreased (-0.06%) to 68.263% when pulling cbdff779a06244932a3005f76b4fe63a64d8ead8 on depop:feature/collect-only-1.4.3 into 3b9dad77d0440cace471aa43d77a4ba619f145bb on django-nose:master.