feat(service): do not start the container if it's already runnnig

* discourse/service/running.sls: verify the state of the container
  before running “launcher:start_cmd”.

discourse/service/running.sls

@@ -9,9 +9,14 @@
 include:
   - {{ sls_service_rebuild }}
 
+{%- set format = '--format "{{.Names}}" ' %}
+{%- set filter = '--filter NAME=app --filter status=running' %}
+
 discourse-service-running-cmd-run:
   cmd.run:
     - name: {{ discourse | traverse('launcher:start_cmd') }}
     - cwd: {{ discourse.directory }}
+    - unless:
+        - test "$(docker ps {{ format }} {{ filter }})" = 'app'
     - require:
       - sls: {{ sls_service_rebuild }}