Add RHEL support to iptables module.

Updates the iptables module so that it uses parameters
to define the package, service, and files used to setup and
configure persistent iptables rules.

With these updates the module should now support both
RHEL and Ubuntu.

Change-Id: I45af4e72065c9baaf1d9a03f18b47f6effdce322
Reviewed-on: https://review.openstack.org/23278
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins