test: fix flaky cluster-net-send

Before this commit, it was possible on Windows for the server's
'connection' handler to be called *after* the client socket's
'connect' handler. This caused the 'message' event to be missed
and the test would never end (timing out in CI). This problem
was more easily reproducible on a low resource (slow CPU)
Windows (2012r2) installation.

This commit waits until both handlers have been called before
sending the handle to the master process.

Fixes: #3957
PR-URL: #4444
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/parallel.status

@@ -7,7 +7,6 @@ prefix parallel
 [true] # This section applies to all platforms
 
 [$system==win32]
-test-cluster-net-send : PASS,FLAKY
 test-cluster-shared-leak : PASS,FLAKY
 test-debug-no-context : PASS,FLAKY
 test-tls-ticket-cluster : PASS,FLAKY

test/parallel/test-cluster-net-send.js

@@ -31,16 +31,22 @@ if (process.argv[2] !== 'child') {
 } else {
  console.error('[%d] worker', process.pid);
 
+ var socket;
+ var cbcalls = 0;
+ function socketConnected() {
+ if (++cbcalls === 2)
+ process.send('handle', socket);
+ }
+
  var server = net.createServer(function(c) {
  process.once('message', function(msg) {
  assert.equal(msg, 'got');
  c.end('hello');
  });
+ socketConnected();
  });
  server.listen(common.PORT, function() {
- var socket = net.connect(common.PORT, '127.0.0.1', function() {
- process.send('handle', socket);
- });
+ socket = net.connect(common.PORT, '127.0.0.1', socketConnected);
  });
 
  process.on('disconnect', function() {