Sync async_nats work with master

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

gateway/vendor/github.com/nats-io/go-nats/util/tls_pre17.go

@@ -0,0 +1,35 @@
+// Copyright 2016 Apcera Inc. All rights reserved.
+// +build go1.5,!go1.7
+
+package util
+
+import (
+	"crypto/tls"
+)
+
+// CloneTLSConfig returns a copy of c. Only the exported fields are copied.
+// This is temporary, until this is provided by the language.
+// https://go-review.googlesource.com/#/c/28075/
+func CloneTLSConfig(c *tls.Config) *tls.Config {
+	return &tls.Config{
+		Rand:                     c.Rand,
+		Time:                     c.Time,
+		Certificates:             c.Certificates,
+		NameToCertificate:        c.NameToCertificate,
+		GetCertificate:           c.GetCertificate,
+		RootCAs:                  c.RootCAs,
+		NextProtos:               c.NextProtos,
+		ServerName:               c.ServerName,
+		ClientAuth:               c.ClientAuth,
+		ClientCAs:                c.ClientCAs,
+		InsecureSkipVerify:       c.InsecureSkipVerify,
+		CipherSuites:             c.CipherSuites,
+		PreferServerCipherSuites: c.PreferServerCipherSuites,
+		SessionTicketsDisabled:   c.SessionTicketsDisabled,
+		SessionTicketKey:         c.SessionTicketKey,
+		ClientSessionCache:       c.ClientSessionCache,
+		MinVersion:               c.MinVersion,
+		MaxVersion:               c.MaxVersion,
+		CurvePreferences:         c.CurvePreferences,
+	}
+}