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

...ecase

[Detailed commit message (if have)]
Impacted TCs num(designed): New 0, update 3, deleted 0
Unit test platform: [tizen]
Unit test result summary:Pass 1, Fail 1,Block 1
Fail:xwalk-1731  uninstall wgt fail, verify if resolved
Block:xwalk-2525 verify if merged