Fix api-ref for list endpoints
Fix api-ref for list endpoints

According to the [1], list endpoints filter also have
``region_id`` parameter which is missing from api-ref.
This patch updates the same in api-ref.

[1]https://github.com/openstack/keystone/blob/master/keystone/api/endpoints.py#L78

Change-Id: I3982c98506f945b47c056ed1c9e5eee673a3662a

mahak/keystone,mahak/keystone,openstack/keystone,mahak/keystone,openstack/keystone,openstack/keystone