unnecessary relation events occur due to order of hosts

Host order is not preserved in python set - resulting in multiple relation-changed events on the provider side

We should upate the provider lib to prevent unnecessary relation-changed events from occuring

Start by locating the provider library code that builds relation data and emits relation-changed events, then reproduce the behavior with hosts supplied in different orders. Done means equivalent host sets produce no unnecessary relation-changed events, while genuine relation changes still do.

Written by the indexing model from the issue text.