Avoid server recreation in case of user_data modification. (#651)

roles/openstack-stack/templates/heat_stack_server.yaml.j2

@@ -134,6 +134,7 @@ resources:
       user_data:
         get_file: user-data
       user_data_format: RAW
+      user_data_update_policy: IGNORE
       metadata:
         group: { get_param: group }
         environment: { get_param: cluster_env }

roles/openstack-stack/templates/heat_stack_server_nofloating.yaml.j2

@@ -119,6 +119,7 @@ resources:
       user_data:
         get_file: user-data
       user_data_format: RAW
+      user_data_update_policy: IGNORE
       metadata:
         group: { get_param: group }
         environment: { get_param: cluster_env }