fix: do not error on unknown os_family grain

If the formula was ran on a system that reported an os_family that
wasn't one of "Debian", "RedHat", "Arch", "Suse" then the map.jinja
template would fail to render with "'NoneType' is not iterable.

This occurs because grains.filter_by will return None when it fails
match the grain to the input dictionary. The value is then blindly
passed into a dict.update() which causes the failure.

In this patch we ensure that the default values, as defined in
defaults.yaml, are always applied when grain matching fails.

firewalld/defaults.yaml

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 # vim: ft=yaml
 ---
+default:
   firewalld:
     enabled: true
     package: firewalld

firewalld/map.jinja

@@ -3,25 +3,18 @@
 
 {#- Start with  defaults from defaults.yaml #}
 {% import_yaml "firewalld/defaults.yaml" as default_settings %}
+{% import_yaml "firewalld/osfamilymap.yaml" as osfamilymap %}
 
-{#-
-Setup variable using grains['os_family'] based logic, only add key:values here
-that differ from whats in defaults.yaml
-#}
-{% set os_family_map = salt['grains.filter_by']({
-    'Debian': {},
-    'RedHat': {},
-    'Arch': {},
-    'Suse': {},
-  }, grain='os_family', merge=salt['pillar.get']('firewalld:lookup'))
-%}
-
-{#- Merge the flavor_map to the default settings #}
-{% do default_settings.firewalld.update(os_family_map) %}
+{% set platform_defaults = salt['grains.filter_by'](default_settings,
+    default='default',
+    merge=salt['grains.filter_by'](osfamilymap, grain='os_family',
+      merge=salt['pillar.get']('firewalld:lookup')
+    )
+) %}
 
 {#- Merge in salt:lookup pillar #}
 {% set firewalld = salt['pillar.get'](
     'firewalld',
-    default=default_settings.firewalld,
+    default=platform_defaults.firewalld,
     merge=True)
 %}

firewalld/osfamilymap.yaml

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+# # vim: ft=yaml
+# os_family defaults
+# only add key:values here that differ from whats in defaults.yaml
+---
+Debian:
+  firewalld: {}
+RedHat:
+  firewalld: {}
+Arch:
+  firewalld: {}
+Suse:
+  firewalld: {}