test: dynamic port in cluster disconnect

Removed common.PORT from test-cluster-disconnect to eliminate the
possibility that a port used in another test will collide
with common.PORT.
PR-URL: #12545
Refs: #12376
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

Author: Sebastian Plesciuc

test/parallel/test-cluster-disconnect.js

@@ -7,14 +7,14 @@ const net = require('net');
 if(cluster.isWorker){
 net.createServer((socket)=>{
 socket.end('echo');
-}).listen(common.PORT,'127.0.0.1');
+}).listen(0,'127.0.0.1');
 
 net.createServer((socket)=>{
 socket.end('echo');
-}).listen(common.PORT+1,'127.0.0.1');
-
+}).listen(0,'127.0.0.1');
 }elseif(cluster.isMaster){
 constservers=2;
+constserverPorts=newSet();
 
 // test a single TCP server
 consttestConnection=(port,cb)=>{
@@ -26,16 +26,18 @@ if (cluster.isWorker) {
 // check result
 socket.on('end',common.mustCall(()=>{
 cb(result==='echo');
+serverPorts.delete(port);
 }));
 });
 };
 
 // test both servers created in the cluster
 consttestCluster=(cb)=>{
 letdone=0;
+constportsArray=Array.from(serverPorts);
 
 for(leti=0;i<servers;i++){
-testConnection(common.PORT+i,(success)=>{
+testConnection(portsArray[i],(success)=>{
 assert.ok(success);
 done+=1;
 if(done===servers){
@@ -51,7 +53,9 @@ if (cluster.isWorker) {
 letonline=0;
 
 for(leti=0,l=workers;i<l;i++){
-cluster.fork().on('listening',common.mustCall(()=>{
+cluster.fork().on('listening',common.mustCall((address)=>{
+serverPorts.add(address.port);
+
 online+=1;
 if(online===workers*servers){
 cb();