downloads: split file and containers (#13581)

Splits the definitions into two dicts, while joining then for now to
preserve the downloads dict.

Update all consumers of the variables, which are roughly:
- manual includes of the download role (which will be removed in the
  short future)
- install tasks using the resolved 'dest' to find the artefacts

This will make further division of the downloads role easier.

roles/kubernetes/node/tasks/install.yml

@@ -1,7 +1,7 @@
 ---
 - name: Install | Copy kubeadm binary from download dir
   copy:
-    src: "{{ downloads.kubeadm.dest }}"
+    src: "{{ downloads_file.kubeadm.dest }}"
     dest: "{{ bin_dir }}/kubeadm"
     mode: "0755"
     remote_src: true
@@ -12,7 +12,7 @@
 
 - name: Install | Copy kubelet binary from download dir
   copy:
-    src: "{{ downloads.kubelet.dest }}"
+    src: "{{ downloads_file.kubelet.dest }}"
     dest: "{{ bin_dir }}/kubelet"
     mode: "0755"
     remote_src: true