OpenSL ES AudioTrack-based player implements IPlayer

Encapsulate the AudioTrack object inside a container for
  it along with an implementation of IPlayer.
Note that at this point the piid and audiomanager reference
  are still stored respectively in CAudioPlayer and Engine,
  only for PLAYER_TYPE_SLES_AUDIOPLAYER_URI_FD players, to be
  consolidated inside GenericPlayer class.

Test: use vendor/google_toolbox/team/audio/cmds/ClPlaybackActivity
Bug 30258418

Change-Id: I88163b05fa1b962b166c5dc33da018ee320ab70a