Work around the system configuration issue that causes NioSocketChannelTest to fail

Motivation:

On some ill-configured systems, InetAddress.getLocalHost() fails.  NioSocketChannelTest calls java.net.Socket.connect() and it internally invoked InetAddress.getLocalHost(), which causes the test failures in NioSocketChannelTes on such an ill-configured system.

Modifications:

Use NetUtil.LOCALHOST explicitly.

Result:

NioSocketChannelTest should not fail anymore.