starts a Pyro4 nameserver in a separate thread
		
		Returns
		-------
			tuple (str, int):
				the host name and the used port

def start(self):
		"""	
		starts a Pyro4 nameserver in a separate thread
		
		Returns
		-------
			tuple (str, int):
				the host name and the used port
		"""
	
		if self.host is None:
			if self.nic_name is None:
				self.host = 'localhost'
			else:
				self.host = nic_name_to_host(self.nic_name)

		uri, self.pyro_ns, _ = Pyro4.naming.startNS(host=self.host, port=self.port)

		self.host, self.port = self.pyro_ns.locationStr.split(':')
		self.port = int(self.port)
		
		thread = threading.Thread(target=self.pyro_ns.requestLoop, name='Pyro4 nameserver started by HpBandSter')
		thread.start()

		if not self.dir is None:
			os.makedirs(self.dir, exist_ok=True)
			self.conf_fn = os.path.join(self.dir, 'HPB_run_%s_pyro.pkl'%self.run_id)

			with open(self.conf_fn, 'wb') as fh:
				pickle.dump((self.host, self.port), fh)
		
		return(self.host, self.port)