Support for ZONE= option

https://git.fedorahosted.org/cgit/initscripts.git/commit/?id=bf931d4f660af978eef8652ad275fcb7bab0e749

Zone means a trust level of the connection,
it is used by firewalld [1] [2].

[1] https://fedoraproject.org/wiki/FirewallD
[2] https://github.com/jpopelka/puppet-firewalld