Allow for custom server addresses when running against SauceLabs.

Sauce Connect can tunnel Selenium traffic, not just Browser traffic.  This is often used in restricted networking environments.

This is supported by running Sauce Connect, then pointing your remote WebDriver to the Sauce Connect machine rather then `ondemand.saucelabs.com`.

This PR lets you specify a seleniumAddress as well as a sauceUser and sauceKey, and still use Sauce with job status updating et al.