[usecase-webapi] Improve Clipboard usecase

- Modify button name "Launch" to "Launch clipboard test" and remove button "Retest"

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: [Andriod]
Test result summary: Pass 1, Fail 0, Blocked 0
Merge pull request #583 from zhangjingx/zhangjingx/misc/clipboard

[usecase-webapi] Improve Clipboard usecase