Fix role schema in trust object

Previously, we weren't doing any validation on the roles attribute of a
trust except to validate that it was an array. A hasty glance, however,
would lead you to believe that it was validating an array of
parameter_types.id_string[1] and so we translated that to the new role
object validation. However, id_string doesn't include some valid role
names like _member_. This patch updates the role name schema to match
parameter_types.name, which is the same as the schema for the main role
object.

[1] http://git.openstack.org/cgit/openstack/keystone/tree/keystone/trust/schema.py?id=62f9e57cd81dc98c5816da9fa483d385b4c1a66c#n41

Change-Id: I83aafc7a96e81a9b6b1056b39cd8c5d23676c014
Closes-bug: #1734871

keystone/tests/unit/test_validation.py

@@ -1485,7 +1485,8 @@ class TrustValidationTestCase(unit.BaseTestCase):
 
     _valid_roles = [{'name': 'member'},
                     {'id': uuid.uuid4().hex},
-                    {'id': str(uuid.uuid4())}]
+                    {'id': str(uuid.uuid4())},
+                    {'name': '_member_'}]
     _invalid_roles = [False, True, 123, None]
 
     def setUp(self):

keystone/trust/schema.py

@@ -19,7 +19,7 @@ _role_properties = {
         'type': 'object',
         'properties': {
             'id': parameter_types.id_string,
-            'name': parameter_types.id_string
+            'name': parameter_types.name
         },
         'minProperties': 1,
         'maxProperties': 1,