Use include/import tasks (#2192)

import_tasks will consume far less memory, so it should be
used whenever it is compatible.

roles/vault/tasks/shared/sync_file.yml

@@ -80,7 +80,7 @@
   set_fact:
     sync_file_results: "{{ sync_file_results|default([]) + [sync_file_result] }}"
 
-- include: sync.yml
+- include_tasks: sync.yml
   when: not (sync_file_no_srcs or sync_file_unneeded)
 
 - name: "Unset local vars to avoid variable bleed into next iteration"