UnitStatus diagnostics checks for status of iptables even though firewalld is enabled.

Issue

• Diagnostics throws errors for UnitStatus as:

# openshift admin diagnostics 
...
...
[Note] Running diagnostic: UnitStatus
       Description: Check status for related systemd units

ERROR: [DS3002 from diagnostic UnitStatus@openshift/origin/pkg/diagnostics/systemd/unit_status.go:55]
       systemd unit atomic-openshift-node depends on unit iptables, which is not loaded.

       iptables is used by nodes for container networking.
       Connections to a container will fail without it.
       An administrator probably needs to install the iptables unit with:

         # yum install iptables

       If it is already installed, you may to reload the definition with:

         # systemctl reload iptables

[Note] Summary of diagnostics execution (version v3.7.14):
[Note] Errors seen: 1