test: improve template value for test message

Include value that cause failure in error message in
test-cluster-master-kill.js.

PR-URL: #16826
Reviewed-By: Gireesh Punathil <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Rich Trott <[email protected]>

Author: d1b1

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

@@ -60,7 +60,8 @@ if (cluster.isWorker) {
   process.once('exit', () => {
     assert.strictEqual(typeof pid, 'number',
                        `got ${pid} instead of a worker pid`);
-    assert.strictEqual(alive, false, 'worker was alive after master died');
+    assert.strictEqual(alive, false,
+                       `worker was alive after master died (alive = ${alive})`);
   });
 
 }