Fix SoundPool.play() looping

This is done by configuring SoundPool for shared memory and fast track.
Previously SoundPool used a streaming track, and looping in streaming
mode relied on the ability to loop the most recently enqueued data.
That 'feature' was lost in the new implementation of streaming, so we're
now switching from streaming mode to shared memory mode.  Shared memory
mode had always been desired, but was blocked by bug 2801375 which is fixed now.

Bug: 10171337
Change-Id: I2a938e3ffafa2a74d5210b4198b50db20ad5da0e