test: refactor flaky net-error-twice

The test was not reliably creating the error event on Windows 2012.

This makes the test more robust by delaying the start of the server
write until nextTick, allowing the connection to close and cause the
error more reliably on Windows 2012.

Fixes: nodejs#4057

Author: Trott

test/parallel/test-net-error-twice.js

@@ -1,33 +1,29 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
-var net = require('net');
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
 
-var buf = new Buffer(10 * 1024 * 1024);
+const buf = new Buffer(10 * 1024 * 1024);
 
 buf.fill(0x62);
 
 var errs = [];
 
-var srv = net.createServer(function onConnection(conn) {
-  conn.write(buf);
+const srv = net.createServer(function onConnection(conn) {
+  process.nextTick(() => { conn.write(buf); });
   conn.on('error', function(err) {
     errs.push(err);
-    if (errs.length > 1 && errs[0] === errs[1])
-      assert(false, 'We should not be emitting the same error twice');
+    if (errs.length > 1)
+      assert(errs[0] !== errs[1], 'Should not get the same error twice');
   });
   conn.on('close', function() {
     srv.unref();
   });
 }).listen(common.PORT, function() {
-  var client = net.connect({ port: common.PORT });
-
-  client.on('connect', function() {
-    client.destroy();
-  });
+  const client = net.connect({ port: common.PORT });
+  client.on('connect', client.destroy);
 });
 
 process.on('exit', function() {
-  console.log(errs);
   assert.equal(errs.length, 1);
 });