test: reland changes from 11c1bae

Reland the changes from commit 11c1bae ("lib: make --debug-port work
with cluster") that were temporarily backed out to cherry-pick commits
from joyent/node.

PR-URL: https://github.com/iojs/io.js/pull/501
Reviewed-By: Bert Belder <bertbelder@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>

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

@@ -2,10 +2,12 @@ var common = require('../common');
 var assert = require('assert');
 var spawn = require('child_process').spawn;
 
-var args = [ common.fixturesDir + '/clustered-server/app.js' ];
+var port = common.PORT + 42;
-var child = spawn(process.execPath, args, {
+var args = ['--debug-port=' + port,
-  stdio: [ 'pipe', 'pipe', 'pipe', 'ipc' ]
+            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;
@@ -61,11 +63,11 @@ process.on('exit', function onExit() {
 
 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),
 ];
 
 function assertOutputLines() {