Comment 1 for bug 1973863

Reason:

we apparently try to concat a string (tripleo_keystone_internal_tls_ca_file[1]) with a list (keystone_volumes) - which is not possible, according to the error message.

The question now is:
- is that one potentially a list, so we'd have to change the default value, or is it always a string, so we'll need to change 3 templates[2] to properly append it to the list?

[1] https://opendev.org/openstack/tripleo-ansible/src/branch/master/tripleo_ansible/roles/tripleo_keystone/defaults/main.yml#L33

[2] https://opendev.org/openstack/tripleo-ansible/src/branch/master/tripleo_ansible/roles/tripleo_keystone/templates