[usecase-cordova][XWALK-2330] Add usecase for Cordova Screenshot plugin

- Use Cordova Screenshot plugin to capture screenshot of xwalkView
- Fail reason: [XWALK-2233](https://crosswalk-project.org/jira/browse/XWALK-2233)

Impacted tests(approved): new 1, update 0, delete 0
Unit test platform: [Android]
Unit test result summary: pass 0, fail 1, block 0