使用Docker启动和停止App Engine实例

I've set up an App Engine project locally using Docker (on OSX), and have been running a server using the usual "gcloud preview app run app.yaml" command. From what I can tell, this keeps creating new images over and over again. After an hour or so of work I end up with something like 30 docker images, each taking 130MB. I've set up an App Engine project locally using