Enable pushgateway persistent storage

Change-Id: Ic850cadd55b842c784d9271dc62cc46b389604a1
Closes-bug: PROD-21073
diff --git a/docker/swarm/stack/monitoring/pushgateway.yml b/docker/swarm/stack/monitoring/pushgateway.yml
index af108a6..461eb0b 100644
--- a/docker/swarm/stack/monitoring/pushgateway.yml
+++ b/docker/swarm/stack/monitoring/pushgateway.yml
@@ -23,8 +23,11 @@
               environment:
                 PUSHGATEWAY_BIND_PORT: ${prometheus:pushgateway:bind:port}
                 PUSHGATEWAY_BIND_ADDRESS: ${prometheus:pushgateway:bind:address}
+                PUSHGATEWAY_DATA_DIR: ${_param:prometheus_pushgateway_data_directory}
               labels:
                 com.mirantis.monitoring: "pushgateway"
               image: ${_param:docker_image_pushgateway}
               ports:
                 - 15012:${prometheus:pushgateway:bind:port}
+              volumes:
+                - ${prometheus:pushgateway:dir:data}:${_param:prometheus_pushgateway_data_directory}