Finish cleaning up module test_role_v2

Some tests in module `test_role_v2` are focused on filters, not roles. Create a
new module, `test_filter_v2`, and move those tests into the new module.
Significantly clean up the moved tests.
The fact that I have to write code like this is due to a design flaw. `EntityFactoryMixin` should have been designed to return more useful objects from the start, not a dicts of attributes. The `EntityReadMixin` has a better design: `read_json` returns a dict of attributes, and `read` returns an object.