When retrieving endpoints from keystone catalog, it's better to use
service_type rather than service_name because the name can be arbitrary
(some operator use custom names) while the service_type should always be
consistent.
Change-Id: I966f2d9f40b8306ba645363a4967139f44d6adde
Signed-off-by: Arnaud Morin <arnaud.morin@gmail.com>