test: update test-net-connect-handle-econnrefused

* var -> const
* assert.equal() -> assert.strictEqual()
* assert.ok(false) -> common.fail()

PR-URL: https://github.com/nodejs/node/pull/9932
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-net-connect-handle-econnrefused.js

@@ -1,18 +1,17 @@
 'use strict';
-var common = require('../common');
-var net = require('net');
-var assert = require('assert');
+const common = require('../common');
+const net = require('net');
+const assert = require('assert');
 
 
 // Hopefully nothing is running on common.PORT
-var c = net.createConnection(common.PORT);
+const c = net.createConnection(common.PORT);
 
 c.on('connect', function() {
-  console.error('connected?!');
-  assert.ok(false);
+  common.fail('connected?!');
 });
 
 c.on('error', common.mustCall(function(e) {
   console.error('couldn\'t connect.');
-  assert.equal('ECONNREFUSED', e.code);
+  assert.strictEqual('ECONNREFUSED', e.code);
 }));