Resolve localhost on start, or specify localhost address in config.

#### Feature Description

Initial resolve of localhost address, or a way to specify localhost address in config.

#### Use Case(s)

On FreeBSD there is no 127.0.0.1 address in jails. A common practice is to give jails 127.0.0.2, 127.0.0.3 and so on addresses for their lo0 interface and specify that address in /etc/hosts as localhost, then every service that bind to localhost will resolve correct address.

IP 127.0.0.1 is hardcoded everywhere in consul sources, and because of that consul won't start in FreeBSD jail.