test: use fixtures module

PR-URL: #15872
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-tls-inception.js

@@ -1,19 +1,18 @@
 'use strict';
 const common = require('../common');
+const fixtures = require('../common/fixtures');
 
 if (!common.hasCrypto)
   common.skip('missing crypto');
 
 const assert = require('assert');
 const tls = require('tls');
 
-const fs = require('fs');
-const path = require('path');
 const net = require('net');
 
 const options = {
-  key: fs.readFileSync(path.join(common.fixturesDir, 'test_key.pem')),
-  cert: fs.readFileSync(path.join(common.fixturesDir, 'test_cert.pem'))
+  key: fixtures.readSync('test_key.pem'),
+  cert: fixtures.readSync('test_cert.pem')
 };
 
 const body = 'A'.repeat(40000);