Comment 1 for bug 1780712

This also impacts the Kubernetes charms, and leads us to use the admin key for everything, rather than the client key, since we don't know (at least with CMR) what username the client key is associated with.

Perhaps it would be sufficient to echo back the service_name that was used over the relation in a new key. Then charmhelpers could be updated to look for that key, and if found, use it instead of local_unit() when calculating the broker_rsp key; and Kubernetes could also use it as the userID value.