test: cleanup test-dgram-error-message-address

* var -> const
* assert.equal() -> assert.strictEqual()
* assert.notEqual() -> assert.notStrictEqual()

Fixes: https://github.com/nodejs/node/issues/8925
PR-URL: https://github.com/nodejs/node/pull/8938
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

test/parallel/test-dgram-error-message-address.js

@@ -1,35 +1,35 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
-var dgram = require('dgram');
+const common = require('../common');
+const assert = require('assert');
+const dgram = require('dgram');
 
 // IPv4 Test
-var socket_ipv4 = dgram.createSocket('udp4');
+const socket_ipv4 = dgram.createSocket('udp4');
 
 socket_ipv4.on('listening', common.fail);
 
 socket_ipv4.on('error', common.mustCall(function(e) {
   assert.strictEqual(e.port, undefined);
-  assert.equal(e.message, 'bind EADDRNOTAVAIL 1.1.1.1');
-  assert.equal(e.address, '1.1.1.1');
-  assert.equal(e.code, 'EADDRNOTAVAIL');
+  assert.strictEqual(e.message, 'bind EADDRNOTAVAIL 1.1.1.1');
+  assert.strictEqual(e.address, '1.1.1.1');
+  assert.strictEqual(e.code, 'EADDRNOTAVAIL');
   socket_ipv4.close();
 }));
 
 socket_ipv4.bind(0, '1.1.1.1');
 
 // IPv6 Test
-var socket_ipv6 = dgram.createSocket('udp6');
+const socket_ipv6 = dgram.createSocket('udp6');
 
 socket_ipv6.on('listening', common.fail);
 
 socket_ipv6.on('error', common.mustCall(function(e) {
   // EAFNOSUPPORT or EPROTONOSUPPORT means IPv6 is disabled on this system.
-  var allowed = ['EADDRNOTAVAIL', 'EAFNOSUPPORT', 'EPROTONOSUPPORT'];
-  assert.notEqual(allowed.indexOf(e.code), -1);
+  const allowed = ['EADDRNOTAVAIL', 'EAFNOSUPPORT', 'EPROTONOSUPPORT'];
+  assert.notStrictEqual(allowed.indexOf(e.code), -1);
   assert.strictEqual(e.port, undefined);
-  assert.equal(e.message, 'bind ' + e.code + ' 111::1');
-  assert.equal(e.address, '111::1');
+  assert.strictEqual(e.message, 'bind ' + e.code + ' 111::1');
+  assert.strictEqual(e.address, '111::1');
   socket_ipv6.close();
 }));