[webapi][XWALK-2450] Fix bug for contactsmanager

- Fix case bug for contactsmanager
- Failure analysis: The Contact.id attribute of type should be string by spec, but get number on crosswalk-9.37.194.0

Impacted tests(approved): new 0, update 4, delete 0
Unit test platform: [Android]
Unit test result summary: pass 3, fail 1, block 0
Merge pull request #877 from yunxliu/yunxliu/webapi/contactsmanager

[webapi][XWALK-2450] Fix bug for contactsmanager