glance-simplestreams-sync service added to the catalog, but no daemon is listening (API not available)

Keystone and glance-simplestreams-sync (g-ss-s) get related so the latter can upload cloud images to the Glance service.

Any identity-service-relation-joined will share that information for Keystone to add the service to its endpoints database:
https://github.com/openstack/charm-glance-simplestreams-sync/blob/master/hooks/hooks.py#L210

It seems that such keymap needs to be shared with Keystone or g-ss-s won't be able to authenticate against the Identity service. But it also looks wrong that an API endpoint exists when it is not reachable.

= Steps to reproduce
juju deploy cs:glance-simplestreams-sync
juju add-relation keystone glance-simplestreams-sync
$ openstack endpoint list --service image-stream -fjson
[
  {
    "Service Type": "product-streams",
    "URL": "http://10.66.111.32",
    "Region": "RegionOne",
    "Enabled": true,
    "Interface": "public",
    "Service Name": "image-stream",
    "ID": "7de458d262ae4af2a9ed3941843edb0c"
  },
  {
    "Service Type": "product-streams",
    "URL": "http://10.66.111.32",
    "Region": "RegionOne",
    "Enabled": true,
    "Interface": "internal",
    "Service Name": "image-stream",
    "ID": "a8ad1dd520b64f0bb01ca659a994e153"
  },
  {
    "Service Type": "product-streams",
    "URL": "http://10.66.111.32",
    "Region": "RegionOne",
    "Enabled": true,
    "Interface": "admin",
    "Service Name": "image-stream",
    "ID": "dc276ee252314d778bcfbf6f0d263957"
  }
]