Relax rules for media apps to stay on RemoteControlDisplay

The playback of notification would make the display of the
 RemoteControlClient disappear from the lockscreen.

Fixed by modifying which AudioFocus owner to consider when
 reevaluating how the RemoteControlDisplay needs to be updated:
 use the first (starting from the top of the AudioFocus stack) that
 uses STREAM_MUSIC, or that uses any other stream type for a short
 period.

Change-Id: Id7cef00c5eed1f6ebfa59634eea8e2c9b2f3f5eb