[wrt][XWALK-1668]Add new audiopolicy testcase

Impacted TCs num(approved): New audiopolicy 7, update multiuser 3, deleted 0
Implacted TCs num(designed): New 2, Update 0, deleted 0
Unit test platform: [tizen]
UT result: Pass:7, Fail 1, block 1
Fail: Crosswalk_AudioPolicy_WebappAudioPlay: two webapp audio can be play at the same time
Block:Crosswalk_AudioPolicy_Muliple_Sinks: No bluetooth headset
Merge pull request #931 from linshen/shenlin/addaudioplicy

[wrt][XWALK-1668]Add new audiopolicy testcase
[wrt] Add subcase and type to tests.xml
[usecase-webapi] Demo for adding pluggable step info

Impacted TCs num(approve): New 0, Update 0, Delete 1
Unit test Platform: Andriod
Unit test result summary: Pass 0, Fail 0, Blocked 0
Merge pull request #896 from JianfengXu/xujf/usecase/step

[usecase-webapi] Demo for adding pluggable step info
Merge pull request #938 from wanghongjuan/wanghongjuan/wrt/subcase

[wrt] Add subcase and type to tests.xml
[wrt-usecase][xwalk-2394] Update TCs due to feature resolved

Impacted TCs num(approved): New 2, Update 4, Delete 0
Unit test Platform: Android
Android test result summary: Pass 6, Fail 0, Block 0
Merge pull request #943 from wanghongjuan/wanghongjuan/usecase/xwalk-2394

[wrt-usecase][xwalk-2394] Update TCs due to feature resolved