test: update output to include exit code & signal

PR-URL: https://github.com/nodejs/node/pull/15945
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com

test/parallel/test-cluster-server-restart-none.js

@@ -10,15 +10,23 @@ if (cluster.isMaster) {
   worker1.on('listening', common.mustCall(() => {
     const worker2 = cluster.fork();
     worker2.on('exit', (code, signal) => {
-      assert.strictEqual(code, 0, 'worker2 did not exit normally');
-      assert.strictEqual(signal, null, 'worker2 did not exit normally');
+      assert.strictEqual(code, 0,
+                         'worker2 did not exit normally. ' +
+                         `exited with code ${code}`);
+      assert.strictEqual(signal, null,
+                         'worker2 did not exit normally. ' +
+                         `exited with signal ${signal}`);
       worker1.disconnect();
     });
   }));
 
   worker1.on('exit', common.mustCall((code, signal) => {
-    assert.strictEqual(code, 0, 'worker1 did not exit normally');
-    assert.strictEqual(signal, null, 'worker1 did not exit normally');
+    assert.strictEqual(code, 0,
+                       'worker1 did not exit normally. ' +
+                       `exited with code ${code}`);
+    assert.strictEqual(signal, null,
+                       'worker1 did not exit normally. ' +
+                       `exited with signal ${signal}`);
   }));
 } else {
   const net = require('net');