Pull all test database options from env variables

Just pulling two and assuming others broke the base configuration I was
using, which uses a different database name and has a password.
Merge branch 'feature/test-db-settings' of https://github.com/takeflight/wagtail into takeflight-feature/test-db-settings

Conflicts:
	runtests.py
Merge branch 'takeflight-feature/test-db-settings'