region config change doesn't update the endpoint listings

the identity-service indicates to keystone to create the endpoint listings for the image-stream service, but if you update the `region` config that endpoint listing is not updated because the relation data is not updated. It seems the charm has some notes about updating the endpoints if use_swift is enabled, but this wasn't the case in my environment.

as a workaround I ran:
juju run -u glance-simplestreams-sync/0 -- relation-set -r identity-service:552 glance-simplestreams-sync/0 region=MyNewRegion

which yielded 6 endpoints in keystone
os endpoint list | grep stream
| 3bf5539a1e7143328ea060aa95d2a1a4 | RegionOne | image-stream | product-streams | True | internal | http://10.216.5.29 |
| 53d934a4fb5347e48151ef0ab152ff1f | MyNewRegion | image-stream | product-streams | True | admin | http://10.216.5.29 |
| a194188be5ea40a0b2b20228bd2f2b6d | MyNewRegion | image-stream | product-streams | True | internal | http://10.216.5.29 |
| aff33e9eae154c388ffea1659580de7c | RegionOne | image-stream | product-streams | True | admin | http://10.216.5.29 |
| d86a0b05e09a41fcb5507b04987661db | RegionOne | image-stream | product-streams | True | public | http://10.216.5.29 |
| e943299cc8294bacbb62e9f2941d1496 | MyNewRegion | image-stream | product-streams | True | public | http://10.216.5.29 |

then I deleted the wrong endpoints:
for e in 3bf5539a1e7143328ea060aa95d2a1a4 aff33e9eae154c388ffea1659580de7c d86a0b05e09a41fcb5507b04987661db; do
   openstack endpoint delete $e
done

charm version is cs:glance-simplestreams-sync-41