fix(runner): prefer sauce to hosted driver when sauceKey is present

Sauce Connect sets up a local Selenium relay at localhost:4445 by
default. Allow users to adjust the `seleniumAddress` to point at this
secure relay instead of the default 'ondemand.saucelabs.com' host while
still using the `sauce` driver provider.

Previously, runner would load the `remote` driver provider if
`seleniumAddress` was configured, even if Sauce credentials were also
configured.