PlaceholderTask.Callback.finished did not correctly suppress CancelledItemListener, and willContinue was unreliable#355

jglick merged 4 commits intojenkinsci:masterjenkinsci/workflow-durable-task-step-plugin:masterfrom

jglick:Callback.finishedjglick/workflow-durable-task-step-plugin:Callback.finishedCopy head branch name to clipboard