[webapi-usecase] Intergation of all subcases to one page for CSSStyleAttribute

- Fail Reason:[XWALK-1326]

Impacted TCs num: New 0, Update 1, Delete 0
Unit test Platform: [Andriod]
Unit test result summary: Pass 0, Fail 1, Blocked 0
[usecase-webapi] Add subcase in tests xml

- Add subcase attribute in <testcase>
- Remove redundant elements in tests xml

Impacted tests(approved): new 0, update 3, delete 0
Unit test platform: [Android]
Unit test result summary: pass 1, fail 2, block 0
[webapi][XWALK-2344] Update test step for gamepad

- To fire gamepadconnected event, need reconnect gamepad.

Impacted TCs num(approved): New 0, Update 3, Delete 0
Unit test Platform: Andriod
Unit test result summary: Pass 3, Fail 0, Blocked 0
[webapi][XWALK-2334] Remove a pop-up during executing "CSS3BG_background-attach$

Impacted tests(approved): New 0, Update 1, Delete 0
Unit test platform: [Android]
Unit test result summary: Pass 1, Fail 0, Block 0
[webapi][XWALK-893] Update the key of iap

- Modify the key of iap app
- Failure analysis: The restore method does not suppot
- Block analysis: "In App Purchase" feature does not allowed in China

Impacted tests(approved): new 6, update 24, delete 0
Unit test platform: [Android]
Unit test result summary: pass 6, fail 2, block 22
Merge pull request #719 from haoxli/haoxli/webapi-usecase-w3c/add-subcase

[usecase-webapi] Add subcase in tests xml
Merge pull request #726 from yunxliu/yunxliu/webapi/update_iap_key

[webapi][XWALK-893] Update the key of iap
Merge pull request #722 from JianfengXu/xujf/2344

[webapi][XWALK-2344] Update test step for gamepad
Merge pull request #723 from minxhuang/hm/webapi/xwalk-2334-hotfix

[webapi][XWALK-2334] Remove pop-up for backgrounds
Merge pull request #714 from JianfengXu/xujf/style/update

[webapi-usecase] Intergation of all subcases to one page for CSSStyleAttribute