test: use fixtures module in tls-handshake-error

PR-URL: nodejs/node#15939
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

Author: Mark Walker

test/parallel/test-tls-handshake-error.js

@@ -1,16 +1,18 @@
 'use strict';
 
 const common = require('../common');
+
 if (!common.hasCrypto)
   common.skip('missing crypto');
 
 const assert = require('assert');
 const tls = require('tls');
-const fs = require('fs');
+
+const fixtures = require('../common/fixtures');
 
 const server = tls.createServer({
-  key: fs.readFileSync(`${common.fixturesDir}/keys/agent1-key.pem`),
-  cert: fs.readFileSync(`${common.fixturesDir}/keys/agent1-cert.pem`),
+  key: fixtures.readKey('agent1-key.pem'),
+  cert: fixtures.readKey('agent1-cert.pem'),
   rejectUnauthorized: true
 }, function(c) {
 }).listen(0, common.mustCall(function() {