Add Tcp behavior inside the endpoint pair

[bokket]

hdfs usually use the New(address string) method to access a namenode node, the user will be the user running the code. If the address is an empty string, it will try to get the NameNode address from the Hadoop configuration file.

I proposal to add endpoint pair. It makes utils.go NewStorage method like

ep,err := endpoint.Parse(opt.Endpoint)
	if err != nil {
		return nil, err
	}

	var address string
	switch ep.Protocol() {
	case endpoint.ProtocolTcp:
		address = ep.Tcp()
	default:
		return nil,services.PairUnsupportedError{Pair: ps.WithEndpoint(opt.Endpoint)}
	}
	store.hdfs,err = hdfs.New(address)
	if err != nil {
		return nil, errors.New("hdfs address is not exist")
	}
	
	return store,nil

[bokket]

Tracking issue for RFC-8

[Xuanwo]

Proposed as #8