Collect swarm metrics on the docker swarm nodes only

Change-Id: I4851af5c4410b1a4d73ba8c3999979aca7eae195
Related-PROD: PROD-25520 (PROD:25520)
diff --git a/docker/meta/telegraf.yml b/docker/meta/telegraf.yml
index 36a437a..53d7378 100644
--- a/docker/meta/telegraf.yml
+++ b/docker/meta/telegraf.yml
@@ -10,7 +10,7 @@
       timeout: 5
       perdevice: true
       total: false
-      gather_services: false
+      gather_services: {% if pillar.docker.swarm is defined %}true{% else %}false{% endif %}
       container_name_exclude: [ "*" ]
       # Measurement filtering
       namepass: [ "docker", "docker_swarm" ]