Parameterized linux_system_codename

Change-Id: Ic527bfa74b4caf7e0bb5d157bfae024f2cf53111
diff --git a/reclass/storage/system/opencontrail_gateway_single.yml b/reclass/storage/system/opencontrail_gateway_single.yml
index 52b2786..30c7043 100644
--- a/reclass/storage/system/opencontrail_gateway_single.yml
+++ b/reclass/storage/system/opencontrail_gateway_single.yml
@@ -1,6 +1,7 @@
 parameters:
   _param:
     opencontrail_gateway_hostname: gtw01
+    opencontrail_gateway_system_codename: trusty
   reclass:
     storage:
       node:
@@ -11,5 +12,5 @@
           - cluster.${_param:cluster_name}.opencontrail.gateway
           params:
             salt_master_host: ${_param:reclass_config_master}
-            linux_system_codename: trusty
+            linux_system_codename: ${_param:opencontrail_gateway_system_codename}
             single_address: ${_param:opencontrail_gateway_address}