Our deployment tests don't need to send E-mail messages. More to the
point, they may perform actions which would like to send E-mail
messages. Make sure, at the network level, they'll be prevented from
doing so. Also allow all connections to egress from the loopback
interface, so that services like mailman can connect to the Exim MTA
Add new rolevars for egress rules to support this, and also fix up
some missing related vars in the iptables role's documentation.