test: switch to use common.fixtures module for fixturesDir

PR-URL: #15821
Reviewed-By: Ryan Graham <r.m.graham@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

test/parallel/test-tls-connect-given-socket.js

@@ -2,16 +2,15 @@
 const common = require('../common');
 if (!common.hasCrypto)
   common.skip('missing crypto');
+const fixtures = require('../common/fixtures');
 
 const assert = require('assert');
 const tls = require('tls');
 const net = require('net');
-const fs = require('fs');
-const path = require('path');
 
 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 server = tls.createServer(options, common.mustCall((socket) => {