Ensure iptables-services is installed when persisting firewall config

iptables-services might not be installed and is required if we're
expecting to be able to start a service called "iptables".

Installing that package is what provides the 'iptables' systemd unit
file.

Change-Id: Ic4ccbc3a0fb531d3d3b7924d22ed0b993a689622

roles/persistent-firewall/tasks/persist/RedHat.yaml

@@ -10,6 +10,13 @@
     content: "{{ ip6tables_rules.stdout }}"
     dest: "/etc/sysconfig/ip6tables"
 
+# This provides the systemd unit file for iptables which might not be installed
+- name: Ensure iptables-services is installed
+  become: yes
+  package:
+    name: iptables-services
+    state: present
+
 - name: Ensure iptables is started
   become: yes
   service: