Sauce Labs integration

We are now able to run unit tests with Sauce Labs.

I created a Sauce Labs account (Open Sauce plan) under the login 'venusjs'. 

When the --sauce-labs command option is passed, a test runner is created to run the tests through Sauce Labs. Before each each test runs, a tunnel has to be created using Sauce Connect. 

With the help of the node package sauce-connect-launcher (https://npmjs.org/package/sauce-connect-launcher), we are able to create a tunnel and run unit test(s) on Sauce Labs.

The caveat is the Open Sauce plan only allows 2 parallel VMs. Thus, we can at most run 2 unit tests at a time.