Return None for missing trust_id in fixture

If the trust_id is unset it raises a KeyError. This is unusual from a
python perspective (if nothing else it should be AttributeError) and
different to all the other attributes of the fixture.

Return None if no trust_id is set on the fixture.

Change-Id: I15d33d77027a188fa47df18387c4610908f8e2d2

keystoneclient/fixture/v2.py

@@ -166,7 +166,7 @@ class Token(dict):
 
     @property
     def trust_id(self):
-        return self.root.setdefault('trust', {})['id']
+        return self.root.setdefault('trust', {}).get('id')
 
     @trust_id.setter
     def trust_id(self, value):

keystoneclient/tests/unit/test_fixtures.py

@@ -35,6 +35,7 @@ class V2TokenTests(utils.TestCase):
         self.assertEqual(user_id, token['access']['user']['id'])
         self.assertEqual(user_name, token.user_name)
         self.assertEqual(user_name, token['access']['user']['name'])
+        self.assertIsNone(token.trust_id)
 
     def test_tenant_scoped(self):
         tenant_id = uuid.uuid4().hex
@@ -48,6 +49,7 @@ class V2TokenTests(utils.TestCase):
         self.assertEqual(tenant_name, token.tenant_name)
         tn = token['access']['token']['tenant']['name']
         self.assertEqual(tenant_name, tn)
+        self.assertIsNone(token.trust_id)
 
     def test_trust_scoped(self):
         trust_id = uuid.uuid4().hex