AudioTrack construction with audio attributes

Store audio attributes in AudioTrack class.
When an AudioTrack is "set" with non null audio
 attributes, derive a stream type that reflects
 the attributes.
When an AudioTrack is "set" without attributes,
 and only has a stream type, derive default
 audio attributes.

Change-Id: I322b91fa9a7e193118960c5e78cdddd85d66f9ad