test: replace common.PORT with 0 in https renegotiation test

Repeated use of common.PORT was resulting in sporadic failures on some
operating systems.

PR-URL: #25599
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: Trott

test/pummel/test-https-ci-reneg-attack.js

@@ -65,8 +65,9 @@ function test(next) {
     res.end('ok');
   });
 
-  server.listen(common.PORT, function() {
-    const args = (`s_client -connect 127.0.0.1:${common.PORT}`).split(' ');
+  server.listen(0, function() {
+    const cmd = `s_client -connect 127.0.0.1:${server.address().port}`;
+    const args = cmd.split(' ');
     const child = spawn(common.opensslCli, args);
 
     child.stdout.resume();