test: use fixtures module

PR-URL: nodejs/node#15843
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

Author: scottjbeck

test/parallel/test-https-localaddress-bind-error.js

@@ -25,12 +25,13 @@ if (!common.hasCrypto)
   common.skip('missing crypto');
 
 const assert = require('assert');
-const fs = require('fs');
 const https = require('https');
 
+const fixtures = require('../common/fixtures');
+
 const options = {
-  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')
 };
 
 const invalidLocalAddress = '1.2.3.4';