The error and completion listeners should be set before
MediaPlayer.prepare() is called, in case of an error
during prepare.
Move the sleep to synchronize the playback of the notification
and the ducking from the MediaPlayer to the playback thread.
Test: play a notification during media playback
Bug: 35855841
Change-Id: I42f01f485f533c1cc84b9d927f0dc594cdb7ec8f