tests/integration: Test that "feedback-ended" is propagated through LfbEvent

When no feedbacks are available (either because the requested event does not exist in the theme or because the system does not have required capabilities, e.g. no vibration motor or LED) feedbackd will emit a "feedback-ended" signal (with reason LFB_EVENT_STATE_REASON_NOT_FOUND) on DBus before completing the event triggering DBus call.

Since the DBus call was not completed yet, LfbEvent will not have learned it's ID yet and therefore not emit it's own "feedback-ended" GObject signal.

In this case the test will timeout since the main loop is never quit.