Suppress authentication error 

Due to a typo I'm able to see my access key (though incorrect).  We should swallow the exception.

```
2015-06-08T07:40:48.854332484Z org.openqa.selenium.UnsupportedCommandException: Sauce Labs Authentication Error.
2015-06-08T07:40:48.854344440Z You used username -> 'xxx' <-- and access key --> 'xxxxxxxx' <-- to authenticate, which are not valid Sauce Labs credentials.
```
