[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
[wrt][XWALK-1731][XWALK-1669]Add pkgcmd backend and webaudio tcs

Implacted TCs num(designed): New 5, Update 0, deleted 0
Unit test platform: [tizen]
Merge pull request #952 from linshen/shenlin/AddTcs-xwalk1773

[wrt][XWALK-1731][XWALK-1669]Add pkgcmd backend and webaudio tcs
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