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/kubespray-defaults/tasks/main.yaml

@@ -1,3 +1,4 @@
+---
 - name: Configure defaults
   debug:
     msg: "Check roles/kubespray-defaults/defaults/main.yml"