[misc-xwalk]Move webaudio sample to xwalk system tests

- Fail Reason: the sample crashes, when repeatedly navigating to webpages with audio playback using WebAudio

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: Andriod
Test result summary: Pass 0, Fail 1, Blocked 0
Merge pull request #524 from JianfengXu/xujf/misc/xwalk

[misc-xwalk] Move WebAudio sample to xwalk system tests