Adds iptables element

Creates a common iptables element where the logic required
to handle iptables rules is consolidated. This change uses
the check (-C) argument to check whether a rule matching
the specification does exist in the selected chain.  Based
on the exit code of the check, a rule is added to iptables.
There is no longer a need to store an .ok file in a stateful
manner.

Change-Id: Ib746ff487a286557a05f9d39ab330853564ef98f
Closes-Bug: 1269151
Co-Authored-By: Ronelle Landy <rlandy@redhat.com>
Merge "Adds iptables element"