message: Simplify executor vlog for not dead nodes.
  Previously a "not dead" node's execution would be reported with "is dead: false" which resulted in folks seeing "is dead" first. Instead don't print anything if the node isn't dead, else print "is dead".
diff: @@ -1618,7 +1618,7 @@ void ExecutorState::Process(TaggedNode tagged_node, int64 scheduled_nsec) {
  if (vlog_) {
  VLOG(1) << "Process node: " << id << " step " << params.step_id << " "
  - << SummarizeNode(*node) << " is dead: " << tagged_node.is_dead
  + << SummarizeNode(*node) << (tagged_node.is_dead ? " is dead" : "")
  << " device: " << device->name();
  }
  @@ -1680,7 +1680,7 @@ void ExecutorState::Process(TaggedNode tagged_node, int64 scheduled_nsec) {
  VLOG(2) << "Async kernel done: " << state->item->node->id()
  << " step " << step_id_ << " "
  << SummarizeNode(*state->item->node)
  - << " is dead: " << state->tagged_node.is_dead
  + << (state->tagged_node.is_dead ? " is dead" : "")
  << " device: " << device->name();
  }
  @@ -1734,7 +1734,7 @@ void ExecutorState::Process(TaggedNode tagged_node, int64 scheduled_nsec) {
  if (vlog_) {
  VLOG(2) << "Synchronous kernel done: " << id << " step "
  << params.step_id << " " << SummarizeNode(*node)
  - << " is dead: " << tagged_node.is_dead
  + << (tagged_node.is_dead ? " is dead: " : "")
  << " device: " << device->name();
  }
  