test: improve the code in test-http-chunked-304

* change the nested functions call to run tests in parallel
* use const and let instead of var
* use common.mustCall to control functions execution
* use assert.strictEqual instead of assert.equal
* use arrow functions

test/parallel/test-http-chunked-304.js

@@ -1,8 +1,8 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
-var http = require('http');
-var net = require('net');
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+const net = require('net');
 
 // RFC 2616, section 10.2.5:
 //
@@ -12,32 +12,35 @@ var net = require('net');
 // Likewise for 304 responses. Verify that no empty chunk is sent when
 // the user explicitly sets a Transfer-Encoding header.
 
-test(204, function() {
-  test(304);
-});
+test(204);
+test(304);
 
-function test(statusCode, next) {
-  var server = http.createServer(function(req, res) {
+function test(statusCode) {
+  const server = http.createServer(common.mustCall((req, res) => {
     res.writeHead(statusCode, { 'Transfer-Encoding': 'chunked' });
     res.end();
     server.close();
-  });
+  }));
 
-  server.listen(0, function() {
-    var conn = net.createConnection(this.address().port, function() {
-      conn.write('GET / HTTP/1.1\r\n\r\n');
+  server.listen(0, common.mustCall(() => {
+    const conn = net.createConnection(
+      server.address().port,
+      common.mustCall(() => {
+        conn.write('GET / HTTP/1.1\r\n\r\n');
 
-      var resp = '';
-      conn.setEncoding('utf8');
-      conn.on('data', function(data) {
-        resp += data;
-      });
+        let resp = '';
+        conn.setEncoding('utf8');
+        conn.on('data', common.mustCall((data) => {
+          resp += data;
+        }));
 
-      conn.on('end', common.mustCall(function() {
-        assert.equal(/^Connection: close\r\n$/m.test(resp), true);
-        assert.equal(/^0\r\n$/m.test(resp), false);
-        if (next) process.nextTick(next);
-      }));
-    });
-  });
+        conn.on('end', common.mustCall(() => {
+          // Connection: close should be in the response
+          assert.strictEqual(/^Connection: close\r\n$/m.test(resp), true);
+          // Make sure this doesn't end with 0\r\n\r\n
+          assert.strictEqual(/^0\r\n$/m.test(resp), false);
+        }));
+      })
+    );
+  }));
 }