Replace TARPIT_HOST with a mock class

okay i have learned my lesson with git branches and run the tests.
To make this a decorator you probably just need to do something like:

```python
@contextlib.contextmanager
def mocked_socket_module(func=None):
    """Return a socket which times out on connect.

    ...
    """
    @functools.wraps(func)
    def replaced_test(*args, **kwargs):
        old_socket = socket.socket
        socket.socket = MockSocket
        try:
            if func is not None:
                func(*args, **kwargs)
            else:
                yield
        finally:
            socket.socket = old_socket

    if func is None:
        replaced_test()
    else:
        return replaced_test
```