[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
No, this checking is not expected. You can use `assert_not_equals(e.added[0], undefined);`