Support Cluster IP

[gangtao]

For proton cluster, need to support cluster ip addresses

1. make sure cluster ip works

conn := proton.OpenDB(&proton.Options{
		Addr: []string{"ip1:8463","ip2:8463,"ip3:8463"},
		Auth: proton.Auth{
			Username: "default",
			Password: "",
		},
	})
	var value int
	conn.QueryRow("SELECT 300").Scan(&value)
	fmt.Println(value)

2. client level load balancer

implement a round robin based query load balancing

[Yibo-Chen13]

Go driver does poll all cluster IP and select the first IP that connects successfully.

func (ch *proton) dial(ctx context.Context) (conn *connect, err error) {
	connID := int(atomic.AddInt64(&ch.connID, 1))
	for num := range ch.opt.Addr {
		if ch.opt.ConnOpenStrategy == ConnOpenRoundRobin {
			num = int(connID) % len(ch.opt.Addr)
		}
		if conn, err = dial(ctx, ch.opt.Addr[num], connID, ch.opt); err == nil {
			return conn, nil
		}
	}
	return nil, err
}