raft storage auto_join with mDNS provider failed

[aubrich]

When configuring vault in HA mode with raft integrated storage the port is append two times to the address. Because the mDNS provider of go-discover returns "host:port" :

https://github.com/hashicorp/go-discover/blob/e89ebd1b2f65c80bb2dd21570c12a2957c9aad82/provider/mdns/mdns_provider.go#L105

And in vault port is always appended to the go-discover result :

vault/vault/raft.go

Line 1234 in 0e227bf

u := fmt.Sprintf("%s://%s:%d", scheme, ip, port)