Add basic tests

This PR adds a basic framework for testing the module, based on https://github.com/garethr/puppet-module-skeleton module.

There are instructions on how to run the tests in README.md under Module Development and Testing but here's a quick start:

* Checkout PR
* ```$ bundle install```
* ```$ rake spec```
* ```$ rake test```

*Important:* This PR only provides basic tests to start the process of testing and linting. More tests are required to harden the module.