[usecase-webapi] Improve Sandbox usecase.

- Remove "Tizen" and "Android" in test purpose.
- Change "Submit Form" to "Submit" in button.

Impacted tests(approved): New 0, Update 1, Delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: Pass 1, Fail 0, Block 0
Merge pull request #547 from minxhuang/hm/misc/usecase-w3c/Sanbox-hotfix

[usecase-webapi] Improve Sandbox usecase.