[usecase-cordova][xwalk-2583] Add usecase for audio pause when app switch to background

- BUG: XWALK-2583/XWALK-2417/XWALK-2597
- Verified on Crosswalk 9.38.208.0

Impacted tests(approved): new 1, update 0, delete 0
Unit test platform: [Android ARM]
Unit test result summary: pass 1, fail 0, block 0
Merge pull request #950 from haoxli/haoxli/usecase/cordova-xwalk-2583

[usecase-cordova][xwalk-2583] Add usecase for audio pause when app switch to background