Add Alertmanager prometheus endpoint and replace ports with variables

Change-Id: I55867b8e483e48204d6393a3542f254556262905
diff --git a/docker/swarm/stack/monitoring.yml b/docker/swarm/stack/monitoring.yml
index 46a2845..bbc2d24 100644
--- a/docker/swarm/stack/monitoring.yml
+++ b/docker/swarm/stack/monitoring.yml
@@ -37,9 +37,12 @@
                 replicas: 2
                 restart_policy:
                   condition: any
+              environment:
+                bind_port: ${prometheus:pushgateway:bind:port}
+                bind_address: ${prometheus:pushgateway:bind:address}
               image: ${_param:docker_image_pushgateway}
               ports:
-                - 15012:9091
+                - 15012:${prometheus:pushgateway:bind:port}
             server:
               networks:
                 - monitoring