[usecase-wrt] Update AudioPolicy test step

[Detailed commit message (if have)]
Impacted TCs num(approved): New 0, update 1, deleted 0
Unit test platform: [tizen]
Unit test result summary:Pass 1, Fail 0,Block 0
Merge pull request #922 from linshen/shenlin/usecase/update-0918

[usecase-wrt] Update AudioPolicy test step
[wrt][xwalk-2540] Update the README description
Merge pull request #924 from wanghongjuan/wanghongjuan/wrt/xwalk-2540

[wrt][xwalk-2540] Update the README description