private String printSourceConnections() {
        StringBuilder sb = new StringBuilder();
        for (String s : proxyServer.getSourceConnections()) {
            sb.append(s).append("\n");
        }
        return sb.toString();
    }
Handles all versions of "getConfig" requests.

@param request a Request
config-proxy/src/main/java/com/yahoo/vespa/config/proxy/ConfigProxyRpcServer.java