Use fqdn with fallback to hostname in jetty.ini

Without this patch, [this line](https://github.com/Seldaek/puppetdb/blob/50c41116f8d0879e7de63350c6a4e80f2b1dc5b6/ext/templates/puppetdb-ssl-setup#L61) is not respected in the generated jetty.ini

I am not sure regarding contributions of such small patches whether I am supposed to create an issue or not in redmine first, but I hope not.