Comment 3 for bug 1927025

Another, perhaps more simple and reliable approach would be to wrap the `write_file()` calls in configure_cert [1] with `with restart_on_change({filename: ...})` [2]. This should only require a few lines of change (plus tests) and handle all potential cases where the certs are updated. The CA file should also be covered, as well.

[1]: https://github.com/juju/charm-helpers/blob/2ec6847/charmhelpers/contrib/openstack/context.py#L1037-L1042

[2]: https://github.com/juju/charm-helpers/blob/2ec6847/charmhelpers/core/host.py#L697