ansible.cfg: Enable the profile_tasks callback plugin

The profile_tasks plugin shows how much time the book run took and
also breaks down an individual view of how much time each task took
to complete.

ansible.cfg

@@ -7,6 +7,7 @@ nocows = 1
 roles_path = roles
 vault_password_file = misc/get-vault-pass.sh
 retry_files_enabled = False
+callback_whitelist = profile_tasks
 
 [ssh_connection]
 pipelining = True