[wrt-usecase] Improve 6 TCs description

- The case WebAppHWKey has an bug xwalk-2654

Impacted TCs num(approved): New 0, Update 6, Delete 0
Unit test Platform: Android
Android test result summary: Pass 5, Fail 1, Block 0
Merge pull request #1005 from wanghongjuan/wanghongjuan/wrt/update-usecase

[wrt-usecase] Improve 6 TCs description