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 }

roles/kubernetes/node/meta/main.yml

@@ -1,3 +1,5 @@
 ---
 dependencies:
- - role: kubernetes/secrets
+  - role: download
+    file: "{{ downloads.kubernetes_kubelet }}"
+  - role: kubernetes/secrets

roles/kubernetes/preinstall/meta/main.yml

@@ -0,0 +1,5 @@
+---
+dependencies:
+  - role: adduser
+    user: "{{ addusers.kube }}"
+    when: ansible_os_family != 'CoreOS'