[webapi] add 16 TCs for gamepad

Impacted Suites: webapi-gamepad-w3c-tests
Impacted TCs num: New 16, Update 0, Delete 0
Unit test Platform: Android
Android test result summary: Pass 1, Fail 15, Blocked 0

Comments:
1. The TCs is base on the Firefox browser.
2. The fail reason is the gamepad can't connect to the android now.
3. The result on Firefox is Pass 14, Fail 2, Blocked 0, fail reason is the timestamp attribute of gamepad does not exist.
Merge pull request #253 from JianfengXu/xujf/webapi/gamepad

[webapi] add 16 TCs for gamepad