add prometheus as last stage

First install Prometheus exporters on new host,
then update monitoring configuration to include new host.

Change-Id: Iba852e7d5a42d79a48481885dd9cde83c5d918f0
diff --git a/ceph-add-node.groovy b/ceph-add-node.groovy
index f2af894..92d61e0 100644
--- a/ceph-add-node.groovy
+++ b/ceph-add-node.groovy
@@ -73,5 +73,8 @@
                 salt.enforceState(pepperEnv, 'I@ceph:radosgw', ['keepalived', 'haproxy', 'ceph.radosgw'], true)
             }
         }
+
+        salt.enforceState(pepperEnv, HOST, 'prometheus')
+        salt.enforceState(pepperEnv, 'I@prometheus', 'prometheus')
     }
 }