test: use dynamic port in 3 test-cluster-worker tests

Remove common.PORT from test-cluster-worker-disconnect,
test-cluster-worker-exit and test-cluster-worker-kill to
eliminate the possibility that a dynamic port used in
another test will collide with common.PORT.

PR-URL: https://github.com/nodejs/node/pull/12443
Ref: https://github.com/nodejs/node/issues/12376
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

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

@@ -7,7 +7,7 @@ if (cluster.isWorker) {
   const http = require('http');
   http.Server(() => {
 
-  }).listen(common.PORT, '127.0.0.1');
+  }).listen(0, '127.0.0.1');
   const worker = cluster.worker;
   assert.strictEqual(worker.exitedAfterDisconnect, worker.suicide);
 

test/parallel/test-cluster-worker-exit.js

@@ -19,7 +19,7 @@ if (cluster.isWorker) {
   server.once('listening', common.mustCall(() => {
     process.exit(EXIT_CODE);
   }));
-  server.listen(common.PORT, '127.0.0.1');
+  server.listen(0, '127.0.0.1');
 
 } else if (cluster.isMaster) {
 

test/parallel/test-cluster-worker-kill.js

@@ -15,7 +15,7 @@ if (cluster.isWorker) {
   const server = http.Server(() => { });
 
   server.once('listening', common.mustCall(() => { }));
-  server.listen(common.PORT, '127.0.0.1');
+  server.listen(0, '127.0.0.1');
 
 } else if (cluster.isMaster) {