[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