Enable prometheus pushgateway persistent storage

Change-Id: If539f26909bd56b168a806773bb9c6574c86bf40
Closes-bug: PROD-21073
diff --git a/tests/pillar/pushgateway.sls b/tests/pillar/pushgateway.sls
index 583fcde..27211d3 100644
--- a/tests/pillar/pushgateway.sls
+++ b/tests/pillar/pushgateway.sls
@@ -5,3 +5,5 @@
       address: 0.0.0.0
       port: 9091
     external_port: 15012
+    dir:
+      data: /opt/pushgateway/data