Add a couple of spec tests for Hiera.

Added some tests, and I have also removed the ```require elasticsearch``` from ```elasticsearch::instance``` The code won't compile otherwise due to circular dependencies. I thought about making the require into an include as this is what we do in the ```elasticsearch::params``` define, but decided it was better to force users to declare the class manually as per the docs or have it not compile. Maybe this isn't be best option?

I've run the all the beaker tests on this branch with the ```require elasticsearch``` removed and they all still pass.