Comment 4 for bug 1809190

Having discussed this bug in the OpenStack team, we've come to the following conclusion:

"Re-write the config-changed hook to reflect the options

i.e. delete bridge mappings/ports that no longer exist and add port mappings that now do exist. This would mean that any additional configuration done directly on the unit (for example by installers to create networking situations that the charm config doesn't handle) would be deleted/broken on the next config-changed hook for any config item.

This ensures that the charm is in full control of the OVS bridges, and that any tinkering is transient and will potentially be scrubbed; OVS is sufficiently verbose in the data you can get to be able to manage this effectively - we could even add extra data to the ports we add so it makes it easier to discover what the charm did vs anything done outside of the charm operations."