Added 'order' argument to randomize the test runner execution order

With this change, we can pass a new command line argument to randomize the execution order of the tests. Here you can see how it works https://github.com/fiunchinho/phpunit-randomizer, but basically you pass the 'order' argument, with the "rand" value.
Optionally, you can tell PHP the seed to use so you get a specific order.
![Executing randomly your tests](http://i.imgur.com/uTWtspK.png)
### Why?
Because this way you can identify if you have tests that share state somehow. If you execute them randomly, this state will no longer be there, and tests will fail, making you aware of the situation.