Queue callback periodic announcement plays over MOH

Steps to reproduce:

1. configure a queue callback
2. Configure a queue, set a name, number, destination on timeout, Callback on 15 second frequency, and accept all other defaults.

When waiting in the queue, the periodic announcement is played concurrently with the music on hold instead of stopping MOH.

If you configure an IVR breakout instead of a Queue Callback breakout, the above issue is not noted.