[webapi][XWALK-1877] Fix bug of sso.

- Block Reason: tizen.sso not implement.

Impacted tests(approved): New 28, Update 0, Delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: Pass 0, Fail 0, Block 28
Merge pull request #656 from minxhuang/hm/webapi/sso-hotfix

[webapi][XWALK-1877] Fix bug of sso.