feat(archive): allow command line arguments without values

* If a service.args value is define as null, only render the param (key) in the systemd unit file

pillar.example

@@ -97,6 +97,7 @@ prometheus:
         service:
           name: prometheus-node-exporter
           args:
+            collector.systemd: null
             web.listen-address: ":9110"
             # collector.textfile.directory: /var/tmp/node_exporter
 

prometheus/archive/install.sls

@@ -132,7 +132,11 @@ prometheus-archive-install-{{ name }}-managed-service:
                {%- if name in ('node_exporter', 'consul_exporter') or 'config_file' not in p.pkg.component[name] %}
                  {%- set args = [] %}
                  {%- for param, value in p.pkg.component.get(name).get('service').get('args', {}).items() %}
+                    {%- if value is not none %}
                       {% do args.append("--" ~ param ~ "=" ~ value ) %}
+                    {%- else %}
+                      {% do args.append("--" ~ param ) %}
+                    {%- endif %}
                  {%- endfor %}
         start: {{ p.pkg.component[name]['path'] }}/{{ name }} {{ args|join(' ') }}
                {%- else %}

test/salt/pillar/default.sls

@@ -87,6 +87,7 @@ prometheus:
       node_exporter:
         service:
           args:
+            collector.systemd: null
             web.listen-address: ":9110"
             # collector.textfile.directory: /var/tmp/node_exporter