_get_barbican_endpoint now uses barbican_endpoint_type config option to
retrieve a correct endpoint from catalog.
This config option is set to 'public' by default and it's a default
value for ServiceCatalog.endpoint_data_for method. It means that the
default behaviour will be the same as before this patch.
Change-Id: Idf4061fe3e35e3c47a993a56b23c0257c92e5cc3