Roles '{flamenco,attract}-user' are now linked to 'subscriber'

All users who get 'subscriber' role automatically get 'flamenco-user' and
'attract-user', and when 'subscriber' is revoked, so are
'{flamenco,attract}-user'.

tests/test_linked_roles.py

@@ -0,0 +1,17 @@
+from abstract_cloud_test import AbstractCloudTest
+
+
+class LinkedRolesTest(AbstractCloudTest):
+    def test_linked_roles(self):
+        user_id = self.create_user(roles=[])
+        db_user = self.fetch_user_from_db(user_id)
+
+        self.badger(db_user['email'], {'subscriber'}, 'grant')
+        db_user = self.fetch_user_from_db(user_id)
+        self.assertEqual({'subscriber', 'flamenco-user', 'attract-user'},
+                         set(db_user['roles']))
+
+        self.badger(db_user['email'], {'subscriber'}, 'revoke')
+        db_user = self.fetch_user_from_db(user_id)
+        self.assertEqual(set(),
+                         set(db_user.get('roles', [])))