The checks `cluster_config_has_changed` and `node_tl_has_changed` use a
state file to store the previous value of the config hash and the
timeline.
Previously the check would fail if something changed, but the new value
would be saved directly. This behavious has changed. The new value
is saved only if `--save` is passed to the check.
The mimics the way [check_pgactivity] manages this kind of checks.
[check_pgactivity]: https://github.com/OPMDG/check_pgactivity
