Add automated tests

@ppp0 @tomaszdurka 

Via [these interesting puppet slides](https://speakerdeck.com/mestachs/how-do-you-puppet) I found a few tools for testing various levels:
- http://puppet-lint.com/ - Verifying the syntax of puppet code
- http://rspec-puppet.com/tutorial/ - Verifying the catalogs of puppet modules
- http://serverspec.org/ - Verifying configuration of actual machines

I would suggest to go with the linting for now, what do you think?
Do you wanna use Travis or our Jenkins?