test: use dynamic port in test-cluster-dgram-reuse

Remove common.PORT from test-cluster-dgram-reuse to eliminate
possibility that a dynamic port used in another test will collide with
common.PORT.

PR-URL: nodejs#12901
Ref: nodejs#12376
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Refael Ackermann <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Daijiro Wachi <[email protected]>

test/parallel/test-cluster-dgram-reuse.js

@@ -16,24 +16,22 @@ if (cluster.isMaster) {
   return;
 }
 
-const sockets = [];
-function next() {
-  sockets.push(this);
-  if (sockets.length !== 2)
-    return;
-
-  // Work around health check issue
-  process.nextTick(() => {
-    for (let i = 0; i < sockets.length; i++)
-      sockets[i].close(close);
-  });
-}
-
 let waiting = 2;
 function close() {
   if (--waiting === 0)
     cluster.worker.disconnect();
 }
 
-for (let i = 0; i < 2; i++)
-  dgram.createSocket({ type: 'udp4', reuseAddr: true }).bind(common.PORT, next);
+const options = { type: 'udp4', reuseAddr: true };
+const socket1 = dgram.createSocket(options);
+const socket2 = dgram.createSocket(options);
+
+socket1.bind(0, () => {
+  socket2.bind(socket1.address().port, () => {
+    // Work around health check issue
+    process.nextTick(() => {
+      socket1.close(close);
+      socket2.close(close);
+    });
+  });
+});