Do not override _param:  with None

Change-Id: Iae1930750b866e31cba79d1d8a0c229076a0f70b
Reviewed-on: https://review.gerrithub.io/370204
Reviewed-by: Dennis Dmitriev <dis.xcom@gmail.com>
Tested-by: Dennis Dmitriev <dis.xcom@gmail.com>
diff --git a/tcp_tests/environment/lab03_ovs_dpdk/common.yml b/tcp_tests/environment/lab03_ovs_dpdk/common.yml
index cbf1423..7434d9c 100644
--- a/tcp_tests/environment/lab03_ovs_dpdk/common.yml
+++ b/tcp_tests/environment/lab03_ovs_dpdk/common.yml
@@ -1,6 +1,6 @@
 parameters:
-  _param:
-  # Put any environment-specific variables here
+  # _param:
+  # Put overrides for any environment-specific variables here
 
   linux:
     network: