Self-host using 'bind' and 'port' from the WSGI config group.

def listen(self):
        """Self-host using 'bind' and 'port' from the WSGI config group."""

        msgtmpl = (u'Serving on host %(host)s:%(port)s')
        host = CONF.wsgi.wsgi_host
        port = CONF.wsgi.wsgi_port
        LOG.info(msgtmpl,
                 {'host': host, 'port': port})
        server_cls = self._get_server_cls(host)
        httpd = simple_server.make_server(host,
                                          port,
                                          self.app,
                                          server_cls)
        httpd.serve_forever()