[test-runner-saucelabs] Add --no-tunnel flag to be compatible with Sauce Connect GitHub action

[justinfagnani]

The Sauce Connect action sets up a Sauce tunnel for a job that can be shared among several processes. This would be good for tests in a monorepo where each package has it's own test script that invokes wtr.

It sounds like adding a --no-tunnel config option might be sufficient, if it makes the SauceLabsLauncher not register with the SauceLabsLauncherManager.