Address standalone kubelet config case

Also place in global vars and do not repeat the kube_*_config_dir
and kube_namespace vars for better code maintainability and UX.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

roles/kubernetes/master/files/namespace.yml

@@ -1,4 +1,4 @@
 apiVersion: v1
 kind: Namespace
 metadata:
-  name: kube-system
+  name: "{{system_namespace}}"