Remove hard-coded 127.0.0.1 loopback address in JDK networking tests

Some of the JDK networking tests use hard-coded 127.0.0.1, loopback address. This works on IPv4 or IPv6&IPv4 network. However, with IPv6-only network, those tests with hard-coded address fail. The following fix would work for IPv4, IPv6&IPv4, and IPv6-only environment:

- so = new Socket("127.0.0.1", port);
+ so = new Socket(InetAddress.getLoopbackAddress(), port);