turn adduser/download roles into meta roles

This should make things a little more composable,
by making these roles meta roles that perform no
actions by default we allow each role to own its own
resources.

roles/kubernetes/master/meta/main.yml

@@ -1,4 +1,8 @@
 ---
 dependencies:
+  - role: download
+    file: "{{ downloads.kubernetes_kubectl }}"
+  - role: download
+    file: "{{ downloads.kubernetes_apiserver }}"
   - { role: etcd }
   - { role: kubernetes/node }