resolvers: use the role ID rather than name to resolve the entity

* the GroupResolver already uses the role ID rather than their name for
  creating reference dictionaries

invenio_users_resources/entity_resolvers.py

@@ -123,9 +123,7 @@ def _resolve(self):
         # Resolves to role name, not id
         role_id = self._parse_ref_dict_id()
         try:
-            return Role.query.filter(
-                Role.name == role_id  # TODO to be changed to role id
-            ).one()
+            return Role.query.filter(Role.id == role_id).one()
         except NoResultFound:
             return {}