Adding a new feature called "stress-test"

This feature is very simple, for a given set of examples, we run the tests in random order for given amount of time.

This is not to be used a performance testing against say a website or a service, but to stress the individual set of tests to uncover any flakey behavior. If a set of tests runs non-stop for 10 mins without a single test flaking out, we can consider a test to be stable.

Thanks!