Fix meta/salt.yml to workaround broken formulas

Change-Id: I6b6fbaaebd3e349bf76aa05cb9eb2004a842d9c5

linux/meta/salt.yml

@@ -12,9 +12,12 @@ grain:
     {%- for service_name, service in pillar.items() %}
       {%- if service.get('_support', {}).get('sphinx', {}).get('enabled', False) %}
         {%- set grains_fragment_file = service_name+'/meta/sphinx.yml' %}
-        {%- macro load_grains_file() %}{% include grains_fragment_file %}{% endmacro %}
-        {%- set grains_yaml = load_grains_file()|load_yaml %}
-        {%- do service_grains.sphinx.doc.update({ service_name: grains_yaml.doc }) %}
+        {%- macro load_grains_file() %}{% include grains_fragment_file ignore missing %}{% endmacro %}
+        {%- set grains = load_grains_file()|load_yaml %}
+        {%- if grains %}
+          {%- set grains_yaml = load_grains_file()|load_yaml %}
+          {%- do service_grains.sphinx.doc.update({ service_name: grains_yaml.doc }) %}
+        {%- endif %}
       {%- endif %}
     {%- endfor %}
     {{ service_grains|yaml(False)|indent(4) }}