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/policy_controller/calico/tasks/main.yml

@@ -1,3 +1,4 @@
+---
 - set_fact:
     calico_cert_dir: "{{ canal_cert_dir }}"
   when: kube_network_plugin == 'canal'