Ansible 2.0 throws a deprecation warning when using bare variables for with_items.
TASK [letsencrypt : generate private keys] *************************************
[DEPRECATION WARNING]: Using bare variables is deprecated. Update your
playbooks so that the environment value uses the full variable syntax
('{{letsencrypt_certs}}'). This feature will be removed in a future release.
Deprecation warnings can be disabled by setting deprecation_warnings=False in
ansible.cfg.
Ansible 2.0 throws a deprecation warning when using bare variables for with_items.