test: Introduce knowledge of FreeBSD jails
FreeBSD jails act differently than your average vm or similar application container. All routing passes through one ip address, which makes things like localhost or 0.0.0.0 resolve differently.
Introduce a helper that allows us to verify if we're in a jail and another one for returning an ip address for localhost.
Also, skip one test instead of trading additional complexity in common.js for one specific user scenario.
R=@indutny