Monitor Prometheus itself

Monitoring Prometheus itself will help to identify issues with the
monitoring setup itself.

Change-Id: I26cfd395831aebffe9f32922c8e795f8df928b9e
diff --git a/charts/prometheus/prometheus.yaml b/charts/prometheus/prometheus.yaml
index 4df43f8..df785d3 100644
--- a/charts/prometheus/prometheus.yaml
+++ b/charts/prometheus/prometheus.yaml
@@ -1145,11 +1145,10 @@
         username: #@ gerrit.username
         password_file: #@ "/etc/secrets/.pwd_{}".format(gerrit.host)
     #@ end
-
-      # - job_name: prometheus
-      #   static_configs:
-      #     - targets:
-      #       - localhost:9090
+    - job_name: prometheus
+      static_configs:
+        - targets:
+          - localhost:9090
 
       # A scrape configuration for running Prometheus on a Kubernetes cluster.
       # This uses separate scrape configs for cluster components (i.e. API server, node)