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/bootstrap-os/tasks/bootstrap-coreos.yml

@@ -49,4 +49,3 @@
   pip:
     name: "{{ item }}"
   with_items: "{{pip_python_modules}}"
-