[webdriver] Integrate webdriver tests from W3C web-platform-tests

- These tests have been verified on Ubuntu
- But they are not verified on Crosswalk platforms
- https://crosswalk-project.org/jira/browse/XWALK-1761 is reported
  to track an issue of XwalkDriver on Crosswalk on Tizen IVI
- The README.md shall be improved with instructions of
  how to run the webdriver tests on Crosswalk platforms