Move mcp_docker_registry to defaults

Change-Id: I8645f8df5290112106ef01801f8db86505c327c9
diff --git a/jenkins/client/job/k8s-test/mcp-k8s-metallb-test-pipeline.yml b/jenkins/client/job/k8s-test/mcp-k8s-metallb-test-pipeline.yml
index 8ebd8eb..3c75156 100644
--- a/jenkins/client/job/k8s-test/mcp-k8s-metallb-test-pipeline.yml
+++ b/jenkins/client/job/k8s-test/mcp-k8s-metallb-test-pipeline.yml
@@ -1,5 +1,6 @@
 parameters:
   _param:
+    # Thise is exactly in-house mirror. Please don't change it to .com
     mcp_docker_registry: 'docker-dev-local.docker.mirantis.net'
   jenkins:
     client: