test: fix race in simple/test-cluster-master-error

Said test checks that the workers shut down when the master errors but it failed
intermittently. Insert a small delay before doing the 'is dead?' check to give
the workers a chance to shut down.

test/simple/test-cluster-master-error.js

@@ -112,6 +112,10 @@ if (cluster.isWorker) {
     // Check that the cluster died accidently
     existMaster = (code === 1);
 
+    // Give the workers time to shut down
+    setTimeout(checkWorkers, 200);
+
+    function checkWorkers() {
       // When master is dead all workers should be dead to
       var alive = false;
       workers.forEach(function(pid) {
@@ -122,6 +126,7 @@ if (cluster.isWorker) {
 
       // If a worker was alive this did not act as expected
       existWorker = !alive;
+    }
   });
 
   process.once('exit', function() {