test: replace fixturesDir with common.fixtures

In test-tls-honorcipherorder.js, use common.fixtures instead of
common.fixturesDir.

PR-URL: #15907
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-tls-honorcipherorder.js

@@ -1,11 +1,11 @@
 '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');
 
 let nconns = 0;
 
@@ -21,8 +21,8 @@ process.on('exit', function() {
 function test(honorCipherOrder, clientCipher, expectedCipher, cb) {
   const soptions = {
     secureProtocol: SSL_Method,
-    key: fs.readFileSync(`${common.fixturesDir}/keys/agent2-key.pem`),
-    cert: fs.readFileSync(`${common.fixturesDir}/keys/agent2-cert.pem`),
+    key: fixtures.readKey('agent2-key.pem'),
+    cert: fixtures.readKey('agent2-cert.pem'),
     ciphers: 'AES256-SHA256:AES128-GCM-SHA256:AES128-SHA256:' +
              'ECDHE-RSA-AES128-GCM-SHA256',
     honorCipherOrder: !!honorCipherOrder