Register existing builders to watch their expirations.

test/test_buildman.py

@@ -199,8 +199,6 @@ class TestEphemeral(unittest.TestCase):
     self.test_executor.stop_builder.assert_called_once_with('1234')
     self.assertEqual(self.test_executor.stop_builder.call_count, 1)
 
-    self.etcd_client_mock.delete.assert_called_once_with(self.mock_job_key)
-
   @async_test
   def test_change_worker(self):
     # Send a signal to the callback that a worker key has been changed