clean shutdown of the nameserver and the config file (if written)

def shutdown(self):
		"""
			clean shutdown of the nameserver and the config file (if written)
		"""
		if not self.pyro_ns is None:
			self.pyro_ns.shutdown()
			self.pyro_ns = None
		
		if not self.conf_fn is None:
			os.remove(self.conf_fn)
			self.conf_fn = None