Exit process if Sauce tunnel fails

The effort here is to fix issues where the Sauce Labs failed to initialize, but the runner exited with status 0:
![](https://camo.githubusercontent.com/f70321f2e2214e079234668297ff93ea5aedc0f9/687474703a2f2f763134642e636f6d2f692f353335666433633330663334392e6a7067)



ref https://github.com/bermi/sauce-connect-launcher/issues/24#issuecomment-41728598