Fix issues 3425035 and 3423785.

- Make sure that STREAM_MUSIC is affected by ringer mode on non voice capable
devices whatever the saved settings say.

- Added a hidden method to AudioManager for VolumePanel to override
the stream selection logic while the panel is showing.

Change-Id: Ib2ff2a7af63decb4e29c45700c41e5058f79d877