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-apps/ansible/tasks/main.yaml

@@ -11,7 +11,7 @@
 - name: Kubernetes Apps | Start Resources
   kube:
     name: kubedns
-    namespace: "{{ kube_namespace }}"
+    namespace: "{{ system_namespace }}"
     kubectl: "{{bin_dir}}/kubectl"
     resource: "{{item.item.type}}"
     filename: "{{kube_config_dir}}/{{item.item.file}}"