[webapi][XWALK-1909] Fix the wrong path of case entry when running "webapi/background"

Impacted tests(approved): New 0, Update 2, Delete 0
Unit test platform: [Android]
Unit test result summary: Pass 2, Fail 0, Block 0
Merge pull request #332 from minxhuang/hm/webapi/xwalk-1909

[webapi][XWALK-1909] Fix the wrong path of case entry when running webapi/background