Up to now, audio focus was implicitly requested and abandoned
when changing the audio mode. This is no longer the case so the
behavior with regards to audio focus can be indepently set by
the CallManager.
The logic implemented here is the same as the one previously used
in AudioService:
- only request audio focus when the ring volume index is > 0
when ringing,
- request focus before setting the audio mode to a mode other
than normal
- abandon audio focus after setting the audio mode to normal
Change-Id: Ia543dc779563dbff09414771fee60e589dfaab9d
4ed37ea81a