common/users: re-add facts_common_admin_users

That's needed by the lxd role

roles/common/tasks/users.yml

@@ -89,3 +89,7 @@
     mode: 0644
   with_items: "{{ dumpfiles.stdout_lines }}"
 
+
+- name: Register the admin users list as a fact
+  set_fact:
+    facts_common_admin_users: "{{ admin_users }}"