daemon: list all the images for private docker-registry reposity and fix the bug 8307

the first commit is for a private docker-registry reposity, there may be just several images, so I think docker can list all the images of a private docker-registry reposity,this commit can fixed it.
the second commit is for bug 8307, when docker restart or stop, docker daemon will not clean up the iptables rules, it because the engine‘s shutdown flag is true before the stopping the container. so this commit can fixed it  .