Deflake tests due to real UserBroadcastDispatcher

Some fixes:
 * Add mock dependencies to QSPanelTest
 * Catch possible exception in UserBroadcastDispatcher. This should only
 happen if we are in a bad state (i.e. non-isolated tests).

Fixes: 155619810
Test: 155619810
Change-Id: I02468cf888633a6a57e200321247653ed6c1e9ee