extend test_ansible_inventory.py with tests to ensure that hostname, fqdn are generated according to expectations to prevent future regressions

[Tiboris]

I think we should also extend https://github.com/neoave/mrack/blob/master/tests/unit/test_ansible_inventory.py with tests to ensure that hostname, fqdn are generated according to expectations to prevent future regressions. Could be a separate PR. Will you write it or should I?

Originally posted by @pvoborni in #152 (comment)