test: remove common.PORT from test-cluster*.js

PR-URL: https://github.com/nodejs/node/pull/12441
Ref: https://github.com/nodejs/node/issues/12376
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-cluster-disconnect-leak.js

@@ -26,4 +26,4 @@ if (cluster.isMaster) {
 
 const server = net.createServer();
 
-server.listen(common.PORT);
+server.listen(0);

test/parallel/test-cluster-disconnect-race.js

@@ -34,6 +34,6 @@ if (cluster.isMaster) {
 
 const server = net.createServer();
 
-server.listen(common.PORT, function() {
+server.listen(0, function() {
   process.send('listening');
 });

test/parallel/test-cluster-process-disconnect.js

@@ -12,7 +12,7 @@ if (cluster.isMaster) {
 } else {
   const net = require('net');
   const server = net.createServer();
-  server.listen(common.PORT, common.mustCall(() => {
+  server.listen(0, common.mustCall(() => {
     process.disconnect();
   }));
 }