[wrt]Update wrt-packertool-tizen-tests script install/uninstall webapp

[Detailed commit message (if have)]
Uninstall fail when install app fail,so update it.
Impacted TCs num(approved): New 0, update 2, deleted  0
Unit test platform: [tizen]
Unit test result summary: Pass 2, Fail 0, Blocked 0
Merge pull request #741 from linshen/wrt/shen/wrt-packertool

[wrt]Update wrt-packertool-tizen-tests script install/uninstall webapp