Adding python-pymysql package in barbican nodes

The patch adds the packages in barbican nodes to be installed
there because barbican dependents on the package but doesn't have
dependency on it.

Change-Id: I6170b268d9de633948932154275250dff981df80
Related-PROD: PROD-21338 (PROD:21338)
diff --git a/barbican/server/cluster.yml b/barbican/server/cluster.yml
index 81ee5af..972c05d 100644
--- a/barbican/server/cluster.yml
+++ b/barbican/server/cluster.yml
@@ -11,3 +11,9 @@
         protocol: ${_param:cluster_internal_protocol}
       database:
         host: ${_param:openstack_database_address}
+  linux:
+    system:
+      package:
+        python-pymysql:
+          fromrepo: ${_param:openstack_version}
+          version: latest