Python2->3 Iteritems Fix

chain for loop was using iteritems which isn't available in Python3
anymore and was throwing an exception when run with Salt on Python3.

iptables/rules.sls

 {%- if grains.get('virtual_subtype', None) not in ['Docker', 'LXC'] %}
 
 {%- set chains = service.get('chain', {}).keys() %}
-{%- for chain_name, chain in service.get('chain', {}).iteritems() %}
+{%- for chain_name, chain in service.get('chain', {}).items() %}
 
 {%- set tables = [] %}
 {%- for rule in chain.get('rules', []) %}