Fix issues with SLPlaybackRateItf interface

Fix issues with SLPlaybackRateItf interface

Set rate was not applied when the AudioTrack is created after
 prepare completed.
Modified playback rate functions in AudioPlayer to pass a
 CAudioPlayer pointer, rather than a pointer to IPlaybackRate
 so the rate update function can be queried from the CAudioPlayer.
Added test that exercises the SLPlaybackRateItf interface as
 well as content looping.
Simplified evaluation of delay between decode and render to
 use a fixed (small) delay that balances time to run the
 event looper, and prevents clicks.

Change-Id: I598e9a96e93ef7a7c3603c8467f9d6b36dacd26d