lib: make --debug-port work with cluster

Make the cluster module intercept the `--debug-port=<port>` command line
switch and replace it with the debug port of the child process.

A happy coincidence of this change is that it finally makes it possible
to run the sequential/test-debug-signal-cluster in parallel, it now no
longer needs the default port numbers.

PR-URL: https://github.com/iojs/io.js/pull/306
Reviewed-By: Miroslav Bajtoš <miroslav@strongloop.com>

lib/cluster.js

@@ -308,7 +308,7 @@ function masterInit() {
     workerEnv.NODE_UNIQUE_ID = '' + id;
 
     for (var i = 0; i < execArgv.length; i++) {
-      var match = execArgv[i].match(/^(--debug|--debug-brk)(=\d+)?$/);
+      var match = execArgv[i].match(/^(--debug|--debug-(brk|port))(=\d+)?$/);
 
       if (match) {
         execArgv[i] = match[1] + '=' + debugPort;

test/sequential/test-debug-signal-cluster.js

@@ -23,10 +23,12 @@ var common = require('../common');
 var assert = require('assert');
 var spawn = require('child_process').spawn;
 
-var args = [ common.fixturesDir + '/clustered-server/app.js' ];
-var child = spawn(process.execPath, args, {
-  stdio: [ 'pipe', 'pipe', 'pipe', 'ipc' ]
-});
+var port = common.PORT + 42;
+var args = ['--debug-port=' + port,
+            common.fixturesDir + '/clustered-server/app.js'];
+var options = { stdio: ['inherit', 'inherit', 'pipe', 'ipc'] };
+var child = spawn(process.execPath, args, options);
+
 var outputLines = [];
 var outputTimerId;
 var waitingForDebuggers = false;
@@ -83,11 +85,11 @@ process.on('exit', function onExit() {
 function assertOutputLines() {
   var expectedLines = [
     'Starting debugger agent.',
-    'Debugger listening on port ' + 5858,
+    'Debugger listening on port ' + (port + 0),
     'Starting debugger agent.',
-    'Debugger listening on port ' + 5859,
+    'Debugger listening on port ' + (port + 1),
     'Starting debugger agent.',
-    'Debugger listening on port ' + 5860,
+    'Debugger listening on port ' + (port + 2),
   ];
 
   // Do not assume any particular order of output messages,