Pass the default worker connection into the started and finished registries

@selwin 

In practice all the registry methods are called with pipelines, but if no connection is passed in when instantiating the registry and the connection stack is empty resolve_connection will raise `NoRedisConnectionException`.

Given that you don't really need an instance level connection when using pipelines perhaps a better solution would be to replace the `connection = pipeline if pipeline is not None else self.connection` pattern with a utility function that raises `NoRedisConnectionException` if neither exist?