Issues with app config and context in tests

[bchopson]

The keg cookiecutter defines a couple of helper methods for patching the app config when testing:
https://github.com/level12/keg-app-cookiecutter/blob/06a8c9467ba29920bd5263b2e3b6d9098f64bff3/%7B%7Bcookiecutter.src_dirname%7D%7D/%7B%7Bcookiecutter.project_pymod%7D%7D/libs/testing.py#L26

Not sure if this is flask or keg related, but after upgrading both packages, the app_config_cli context manager doesn't actually change the config in CLI tests, while the app_config context manager does. I can get app_config_cli to work when I set app_cls on the CLI test base class, but then accessing the DB session fails.