Break up TestCollectionViewSet into a number of test cases each corresponding to an endpoint (bug 913210).

It may be easiest to evaluate this PR by looking at `test_views` at the commit itself:

https://github.com/chuckharmston/zamboni/blob/5bf0f4548a235277dc7c16524823cb1d2b0a8084/mkt/collections/tests/test_views.py

r? @diox