[webapi] Add audio playback for audiosytem

- Fail Reason: Its not playing using pulseaudio by launching from xwalk-launcher.

Impacted TCs num(approved): New 0, Update 8, Delete 0
Unit test Platform: [Tizen IVI]
Unit test result summary: Pass 0, Fail 8, Blocked 0
`sound_5.oga` is very short; not sure if it is OK for this test.

Another, you can specify `src` of `<audio>`, no need `<source>`.