Replace host splitting with net.SplitHostPort to avoid splitting ipv6 formats

[Skarlso]

What would you like to be added:

Instead of

	host := hostport
	i := strings.Index(hostport, ":")
	if i > 0 {
		host = hostport[:i]
	}

use net.SplitHostPort.

Why is this needed:

IPv6 Support is requiring this.