public Promise<Void> gracefullyShutdownClientChannels() {
        return gracefullyShutdownClientChannels(ShutdownType.SHUTDOWN);
    }
TODO: Change this class to be an instance per-port.
So that then the configuration can be different per-port, which is need for the combined FTL/Cloud clusters.
<p>
User: michaels@netflix.com
Date: 3/6/17
Time: 12:36 PM
zuul-core/src/main/java/com/netflix/zuul/netty/server/ClientConnectionsShutdown.java