cleanup string formatting in modules.iptables

************* Module salt.modules.iptables
salt/modules/iptables.py:489: [E1305(too-many-format-args), check] Too many arguments for format string
salt/modules/iptables.py:527: [E1305(too-many-format-args), check_chain] Too many arguments for format string
Merge pull request #14572 from hulu/iptables-str-fmt-fixes

cleanup string formatting in modules.iptables