[wrt]XWALK-1731 Update test.xml to approve the backend tcs

[Detailed commit message (if have)]
Impacted TCs num(approved): New 0, update 3 , deleted 0
Unit test platform: [tizen]
Test Result: Pass 3, Fail 0
Merge pull request #1011 from linshen/shenlin/update-1731-to-approved

[wrt]XWALK-1731 Update test.xml to approve the backend tcs