test: refactor pummel/test-net-many-clients

* Use port 0 instead of `common.PORT`.
* Reduce `concurrent` from 100 to 50 and `connections_per_client` from 5
  to 3. This is to avoid side effects from other tests. Prior to this
  change, running this along with test-keep-alive would result in
  failures on my local setup, apparently due to network throttling.
* Remove unnecessary `console.log()` and improve remaining
  `console.log()` to provide clearer information.

PR-URL: #25485
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/pummel/test-net-many-clients.js

@@ -20,30 +20,29 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 'use strict';
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const net = require('net');
 
 // settings
 const bytes = 1024 * 40;
-const concurrency = 100;
-const connections_per_client = 5;
+const concurrency = 50;
+const connections_per_client = 3;
 
 // measured
 let total_connections = 0;
 
 const body = 'C'.repeat(bytes);
 
 const server = net.createServer(function(c) {
-  console.log('connected');
   total_connections++;
-  console.log('#');
+  console.log('connected', total_connections);
   c.write(body);
   c.end();
 });
 
-function runClient(callback) {
-  const client = net.createConnection(common.PORT);
+function runClient(port, callback) {
+  const client = net.createConnection(port);
 
   client.connections = 0;
 
@@ -79,17 +78,17 @@ function runClient(callback) {
     assert.ok(!client.fd);
 
     if (this.connections < connections_per_client) {
-      this.connect(common.PORT);
+      this.connect(port);
     } else {
       callback();
     }
   });
 }
 
-server.listen(common.PORT, function() {
+server.listen(0, function() {
   let finished_clients = 0;
   for (let i = 0; i < concurrency; i++) {
-    runClient(function() {
+    runClient(server.address().port, function() {
       if (++finished_clients === concurrency) server.close();
     });
   }