Add testingbot.com (selenium grid) support

Hi,

We'd like to send a pull-request to offer testingbot.com support next to saucelabs (and browserstack #126)

What would be the best way to approach this? Something similar to https://github.com/defunctzombie/zuul/blob/master/lib/SauceBrowser.js ?

[defunctzombie]

yep, something similar to that would be the first step :)

[alexbardas]

Are there any updates here? Would be great to have support for other 3rd party solutions.