Allocate two ports to each worker.

lib/util/cliutil.js

@@ -9,3 +9,12 @@ module.exports.allUnknownArgs = function(args) {
 module.exports.lastArg = function(args) {
   return args[args.length - 1]
 }
+
+module.exports.range = function(from, to) {
+  var items = []
+    , i
+  for (i = from; i <= to; ++i) {
+    items.push(i)
+  }
+  return items
+}