proxy address format is not IPv6 compatible

[seeder]

Overview of the Issue

consul connect proxy public address is not escaped correctly for IPv6 addresses when making connection to upstream.

There is a Sprintf in https://github.com/hashicorp/consul/blob/master/connect/proxy/config.go which doesn't take into account a proper format for IPv6 addresses ( line 116 )

Reproduction Steps

Steps to reproduce this issue, eg:

1. start a connect proxy for a service, make the proxy register listen under IPv6 address consul connect proxy -service postgres -service-addr 172.17.0.3:5432 -listen [fc01::1]:15432 -register
2. start a connect proxy upstream to access the service consul connect proxy -service web -upstream postgres:5432
3. View error on the proxy which is trying to establish connect (web side)

[ERR] failed to dial: dial tcp: address fc01::1:15432: too many colons in address

Consul info for both Client and Server

Client info

 consul info
agent:   
        check_monitors = 0
        check_ttls = 2
        checks = 5
        services = 5
build:   
        prerelease =
        revision = c97c712e
        version = 1.4.2

Server info

 consul info
agent:   
        check_monitors = 0
        check_ttls = 2
        checks = 5
        services = 5
build:   
        prerelease =
        revision = c97c712e
        version = 1.4.2

Operating system and Environment details

Ubuntu 18.04

[seeder]

is there any chance that this patch gets merged?

looks like it was an easy fix, but there is no will to actually close this blocker bug