[webapi][xwallk-2123] Sync tests update for web testing service

- Update error name form NotSupportedError to TypeError, changes merged in https://github.com/crosswalk-project/crosswalk-test-suite/pull/828
Merge pull request #861 from haoxli/haoxli/webapi/xwalk-2123-py

[webapi][xwallk-2123] Sync tests update for web testing service