Add xenial param to prx and sl nodes

Change-Id: I71fc35b027496844cb509845d07ab5cc4a4567fb
diff --git a/classes/cluster/virtual-mcp-ocata-ovs/infra/config.yml b/classes/cluster/virtual-mcp-ocata-ovs/infra/config.yml
index 40b4eaf..0f2908c 100644
--- a/classes/cluster/virtual-mcp-ocata-ovs/infra/config.yml
+++ b/classes/cluster/virtual-mcp-ocata-ovs/infra/config.yml
@@ -88,6 +88,8 @@
         openstack_proxy_node01:
           classes:
           - cluster.virtual-mcp-ocata-ovs.openstack.proxy
+          params:
+            linux_system_codename: xenial
         stacklight_server_node01:
           classes:
           - system.influxdb.server.single