Split/view test setup

@doctoryes mostly style changes, sorry. The important changes: factories.py, common.py not hardcoding slash separarated ck type, fixing course id collision in test_navigation.py (only applies to old mongo).

This fixes the unit test & acceptance test failures for using `create_course` instead of `create_item` still using only old mongo.

LMS-11441

I may add to this as I fix acceptance tests for split or create a separate PR. I wanted to show momentum on our JIRA board.
Do you need this change anymore? I'm worried that it will obscure other instances of the test dbs not being cleaned up.