Code review comment for ~rharding/interface-grafana-source:add-mysql-support

Thanks, I've looked into this and it seems it's related into the way the grafana datasources code works. It detects that it's already been done and when you break the relation it doesn't do any deleting. I'll have to dive into this a bit as I'm a bit fuzzy on how the internal code tracking the datasources (not in the grafana db itself) works.