Add config option to disable use of sauce-connect

[treyturner]

A question I posed to the geb-user mailing list:

Is it possible to skip sauce-connect initialization completely when using geb/saucelabs/gradle plugins?

Response from @erdi:

Yes, in your build script you can do:
openSauceTunnelInBackground.enabled = false
closeSauceTunnel.enabled = false

This will skip the tunnel related tasks.

We should probably add an option to the DSL to specify that you don't want to use the tunnel, something like:

sauceLabs.useTunnel = false

Would you mind opening an issue for this in the tracker?

Thanks for the help!