Store the project domain ID in the Token object

The project domain ID is needed if a client needs to rescope a token
using the Identity V3 endpoint, so make it available.

Change-Id: I18a9d42906cb2116903600d47880ebdfff1e1ef9
Partial-bug: #1660436

openstack_auth/user.py

@@ -105,6 +105,7 @@ class Token(object):
         project['name'] = auth_ref.project_name
         project['is_admin_project'] = getattr(auth_ref, 'is_admin_project',
                                               False)
+        project['domain_id'] = getattr(auth_ref, 'project_domain_id', None)
         self.project = project
         self.tenant = self.project