test: clean up net server try ports test

* Replace var's with const and let
* Replace boolean flags with common.mustCall()
* Using stricter comparisons
* Fixed typo in comment

PR-URL: #8458
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-net-server-try-ports.js

@@ -1,52 +1,24 @@
 'use strict';
-// This tests binds to one port, then attempts to start a server on that
+// This test binds to one port, then attempts to start a server on that
 // port. It should be EADDRINUSE but be able to then bind to another port.
-require('../common');
-var assert = require('assert');
-var net = require('net');
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
 
-var server1listening = false;
-var server2listening = false;
-var server2eaddrinuse = false;
+const server1 = net.Server();
 
-var server1 = net.Server(function(socket) {
-  socket.destroy();
-});
+const server2 = net.Server();
 
-var server2 = net.Server(function(socket) {
-  socket.destroy();
-});
-
-var server2errors = 0;
-server2.on('error', function(e) {
-  server2errors++;
-  console.error('server2 error');
-
-  if (e.code == 'EADDRINUSE') {
-    server2eaddrinuse = true;
-  }
-
-  server2.listen(0, function() {
-    console.error('server2 listening');
-    server2listening = true;
+server2.on('error', common.mustCall(function(e) {
+  assert.strictEqual(e.code, 'EADDRINUSE');
 
+  server2.listen(0, common.mustCall(function() {
     server1.close();
     server2.close();
-  });
-});
+  }));
+}));
 
-
-server1.listen(0, function() {
-  console.error('server1 listening');
-  server1listening = true;
+server1.listen(0, common.mustCall(function() {
   // This should make server2 emit EADDRINUSE
   server2.listen(this.address().port);
-});
-
-
-process.on('exit', function() {
-  assert.equal(1, server2errors);
-  assert.ok(server2eaddrinuse);
-  assert.ok(server2listening);
-  assert.ok(server1listening);
-});
+}));