Triggering a fixed hook as part of upgrade-charm

[Tom Haddon]

Hi Folks,

If we have a problem with a particular hook, and fix that, we can
upgrade-charm to rollout the fixed version of the charm. However, how do
we actually fire the hook in question? I'm looking for this in terms of
the "right way"™ as there are a few manual ways of doing this I can
think of. Should we include the hook we want to run in the upgrade-charm
hook? If the hook is a relation-changed, we don't necessarily want to do
anything invasive to trigger that hook from being fired (such as
changing the environment) we just want the hook to be rerun.

Thanks, Tom