void stop() {
        Event.stopping("configproxy", "shutdown rpcServer");
        if (rpcServer != null) rpcServer.shutdown();
        Event.stopping("configproxy", "cancel configClient");
        configClient.shutdown();
        Event.stopping("configproxy", "flush");
        flush();
        Event.stopping("configproxy", "close fileDistribution");
        fileDistributionAndUrlDownload.close();
        Event.stopping("configproxy", "stop complete");
    }
A proxy server that handles RPC config requests. The proxy can run in two modes:
'default' and 'memorycache', where the last one will not get config from an upstream
config source, but will serve config from memory cache only.

@author hmusum
config-proxy/src/main/java/com/yahoo/vespa/config/proxy/ProxyServer.java