test: use strictEqual consistently in agent test

Update parallel/test-http-agent-getname to use assert.strictEqual()
consistently and const-ify variables while we're here.

PR-URL: #6654
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-http-agent-getname.js

@@ -1,13 +1,13 @@
 'use strict';
 
 require('../common');
-var assert = require('assert');
-var http = require('http');
+const assert = require('assert');
+const http = require('http');
 
-var agent = new http.Agent();
+const agent = new http.Agent();
 
 // default to localhost
-assert.equal(
+assert.strictEqual(
   agent.getName({
     port: 80,
     localAddress: '192.168.1.1'
@@ -16,13 +16,13 @@ assert.equal(
 );
 
 // empty
-assert.equal(
+assert.strictEqual(
   agent.getName({}),
   'localhost::'
 );
 
 // pass all arguments
-assert.equal(
+assert.strictEqual(
   agent.getName({
     host: '0.0.0.0',
     port: 80,