Remove 'python-apt' before testing the 'apt_repository' module. The
'apt_repository' module has the smarts to auto-install python-apt. The
integration test will now assert the correct auto-install behavior.
Tests several ways to specify the repository. For every repo added, the test
asserts that:
* the apt-cache was updated as expected (depends on `update_cache` parameter)
* the PPA key was installed (depends on `repo` format)
