better handling of port in use errors with cluster

src/webserver.js

@@ -108,7 +108,11 @@ if(nconf.get('ssl')) {
 		server.on("error", function(err){
 			if (err.code === 'EADDRINUSE') {
 				winston.error('NodeBB address in use, exiting...');
-				process.exit(1);
+				if (cluster.isWorker) {
+					cluster.worker.kill();
+				} else {
+					process.exit(0);
+				}
 			} else {
 				throw err;
 			}