choose between gce and aws cloud providers

roles/kubernetes/preinstall/tasks/main.yml

@@ -46,6 +46,11 @@
     owner: kube
   when: ansible_service_mgr in ["sysvinit","upstart"]
 
+- name: check cloud_provider value
+  fail:
+    msg: "If set the 'cloud_provider' var must be set eithe to 'gce' or 'aws'"
+  when: cloud_provider is defined and cloud_provider not in ['gce', 'aws']
+
 - name: Create cni directories
   file:
     path: "{{ item }}"