Fix ProxyTunnel to always use the IP-address instead of the localhost (…

…#1563)

Motivation:

ProxyTunnel was returning the `localhost` hostname instead of the IP-address, which in some configurations
where the IPv4 is preferred but the DNS resolves in both IPv4 and IPv6 for the loopback hostname,
cause connectivity issues.

Modifications:

Modified the ProxyTunnel to always return the IP-address for the clients to connect to.

Result:

More stable test.

servicetalk-http-netty/src/test/java/io/servicetalk/http/netty/ProxyTunnel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2020 Apple Inc. and the ServiceTalk project authors
+ * Copyright © 2020-2021 Apple Inc. and the ServiceTalk project authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -61,6 +61,7 @@ public void close() throws Exception {
 
     HostAndPort startProxy() throws IOException {
         serverSocket = new ServerSocket(0, 50, getLoopbackAddress());
+        final InetSocketAddress serverSocketAddress = (InetSocketAddress) serverSocket.getLocalSocketAddress();
         executor.submit(() -> {
             while (!executor.isShutdown()) {
                 final Socket socket = serverSocket.accept();
@@ -86,7 +87,8 @@ HostAndPort startProxy() throws IOException {
             }
             return null;
         });
-        return HostAndPort.of((InetSocketAddress) serverSocket.getLocalSocketAddress());
+
+        return HostAndPort.of(serverSocketAddress.getAddress().getHostAddress(), serverSocketAddress.getPort());
     }
 
     void badResponseProxy() {