test:replace common.fixturesDir with commonfixtures

PR-URL: nodejs/node#15832
Reviewed-By: Ryan Graham <r.m.graham@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-tls-net-connect-prefer-path.js

@@ -1,5 +1,6 @@
 'use strict';
 const common = require('../common');
+const fixtures = require('../common/fixtures');
 
 // This tests that both tls and net will ignore host and port if path is
 // provided.
@@ -28,8 +29,8 @@ function mkServer(lib, tcp, cb) {
   const args = [handler];
   if (lib === tls) {
     args.unshift({
-      cert: fs.readFileSync(`${common.fixturesDir}/test_cert.pem`),
-      key: fs.readFileSync(`${common.fixturesDir}/test_key.pem`)
+      cert: fixtures.readSync('test_cert.pem'),
+      key: fixtures.readSync('test_key.pem')
     });
   }
   const server = lib.createServer(...args);