Prioritize checking consumer context cancellation

Tests expect that as soon as eventer shuts down immediately on context
cancellations; but golang does not guarantee priority when multiple
pending channels are ready in a select statement.

client/client_test.go

@@ -549,7 +549,7 @@ func waitTilNodeReady(client *Client, t *testing.T) {
 
 func TestClient_SaveRestoreState(t *testing.T) {
 	t.Parallel()
-	ctestutil.ExecCompatible(t)
+
 	s1, _ := testServer(t, nil)
 	defer s1.Shutdown()
 	testutil.WaitForLeader(t, s1.RPC)
@@ -573,6 +573,7 @@ func TestClient_SaveRestoreState(t *testing.T) {
 	alloc1.Job.TaskGroups[0].Tasks[0].Config = map[string]interface{}{
 		"run_for": "10s",
 	}
+	alloc1.ClientStatus = structs.AllocClientStatusRunning
 
 	state := s1.State()
 	if err := state.UpsertJob(100, job); err != nil {

drivers/shared/eventer/eventer.go

@@ -81,6 +81,15 @@ func (e *Eventer) iterateConsumers(event *drivers.TaskEvent) {
 	e.consumersLock.Lock()
 	filtered := e.consumers[:0]
 	for _, consumer := range e.consumers {
+
+		// prioritize checking if context is cancelled prior
+		// to attempting to forwarding events
+		// golang select evaluations aren't predictable
+		if consumer.ctx.Err() != nil {
+			close(consumer.ch)
+			continue
+		}
+
 		select {
 		case <-time.After(consumer.timeout):
 			filtered = append(filtered, consumer)