Add tests for glance/notifier/notify_kombu

Add tests for glance/notifier/notify_kombu in
RabbitStrategyTestCase class.
Tests for:
- _close()
- _connect()
- time.sleep() in reconnect()
- processing KombuMaxRetriesReached error in _notify()

Change-Id: I39805ce460ce2b71dcb05e63cb898c5569d726b0
Merge "Add tests for glance/notifier/notify_kombu"