Adding yamllinter to ci steps (#1556)

* Adding yaml linter to ci check

* Minor linting fixes from yamllint

* Changing CI to install python pkgs from requirements.txt

- adding in a secondary requirements.txt for tests
- moving yamllint to tests requirements

roles/kubernetes-apps/ansible/templates/kubedns-autoscaler-sa.yml

@@ -1,3 +1,4 @@
+---
 # Copyright 2016 The Kubernetes Authors. All rights reserved
 #
 # Licensed under the Apache License, Version 2.0 (the "License");