[usecase-wrt][XWALK-2525][XWALK-1731][XWALK-1668]update test step for usecase

[Detailed commit message (if have)]
Impacted TCs num(designed): New 0, update 3, deleted 0
Unit test platform: [tizen]
Unit test result summary:Pass 0, Fail 2,Block 1
Fail:xwalk-1731  uninstall wgt fail, verify if resolved
Fail:xwalk-1668 webapp audio can not suspend when paplay playing phone audio.
Block:xwalk-2525 verify if merged
Merge pull request #909 from linshen/shenlin/update-usecase-0917

[usecase-wrt][XWALK-2525][XWALK-1731][XWALK-1668]update test step for us...