Have the service catalog ignore empty urls

The service catalog was ignoring None for URLs, but not empty
strings.  This change should hit both cases.

Change-Id: I72ec344ff3f24fcd960023be5e39294c6b12ce34

openstack/auth/service_catalog.py

@@ -54,7 +54,7 @@ class ServiceCatalog(object):
                 if not filtration.match_visibility(endpoint.get('interface')):
                     continue
                 url = endpoint.get('url')
-                if url is not None:
+                if url:
                     eps += [url]
         return eps