Integration tests break when user changes new driver version

[tmattsso]

If I update the driver version file to something new (which I had to do, because the published version drags behind the repo currently), the automatic driver download fails and the tests fail because of wrong driver version.

It reads the new conf correctly, but already finds an old driver in the .driver folder. That file and the config have hash mismatches, so the plugin ignores the new file, and uses the old one. The old one will probably not work, because the users browser is newer than the old driver.

Also, NONE of this is documented in the readme file.

Suggestion:

1. document what webdrivers.xml is
2. document how to update it
3. document what to do if update fails (delete the .driver folder)

The vaadin plugin could also maybe delete that directory.