Set custom UserFactory for tp pytest fixture

[mblayman]

Hi, y'all! I set up pytest on my Django project this evening. I was/am hoping to replace my use of the unittest-derived TestCase defined in this project with the tp fixture made available by pytest plugin.

Judging by plugin.py, it looks like it's not possible to set a custom UserFactory for the fixture like you can for the TestCase.

It would be nice to be able to define this for the tp fixture too. Without this ability, tp.make_user is limited to the User.objects.create_user call on https://github.com/revsys/django-test-plus/blob/master/test_plus/test.py#L266.

One possible thought to fix this would be to expose a pytest configuration option that would set a module path to the UserFactory (e.g., myapp.factories.UserFactory) and load that class onto the t.user_factory attribute when the tp fixture creates the TestCase.

Thanks for the great project. I really enjoy the extensions that test plus provides.