The fake_notifier uses module globals and also needs careful stub and
reset calls to work properly. This patch wraps the fake_notifier into a
proper Fixture that automates the complexity.
This is fairly rage patch but it does not change any logic just redirect
calls from the fake_notifier to the new NotificationFixture
Change-Id: I456f685f480b8de71014cf232a8f08c731605ad8