[webapi][XWALK-2101] Add audio playback for audiosystem.

- Fail Reason: the num of streams is 0.

Impacted TCs num: New 0, Update 1, Delete 0
Unit test Platform: [Tizen IVI]
Unit test result summary: Pass 0, Fail 1, Blocked 0
Merge pull request #796 from JianfengXu/xujf/audiosystem/2101

[webapi][XWALK-2101] Add audio playback for audiosystem.