fix: clean up port-reserver.pid and the parent dir when the container is removed

In the current implementation, when a container is started with the -p
option, a `sleep infinity` process is launched to reserve host ports.

The PID of this process is stored in
`/run/nerdctl/<namespace>/<container ID>/port-reserver.pid`.

When the container is removed, the following file and directory are
expected to be cleaned up.

- /run/nerdctl/<namespace>/<container ID>/port-reserver.pid
- /run/nerdctl/<namespace>/<container ID>/

However, currently they are not removed as shown below:

```
$ sudo nerdctl run -d --name nginx -p 81:80 nginx
ca1552d394cd8efcc5adcff9434deb4f3ead569d168f6e31bea1ae965db8b919

$ ls /run/nerdctl/default/ca1552d394cd8efcc5adcff9434deb4f3ead569d168f6e31bea1ae965db8b919
port-reserver.pid

$ sudo nerdctl rm -f nginx
nginx

$ ls /run/nerdctl/default/ca1552d394cd8efcc5adcff9434deb4f3ead569d168f6e31bea1ae965db8b919
port-reserver.pid
```

Therefore, this commit ensures that they are removed when the container is
removed.

Signed-off-by: Hayato Kiwata <dev@haytok.jp>

Author: haytok

pkg/ocihook/ocihook.go

@@ -748,6 +748,9 @@ func onPostStop(opts *handlerOpts) error {
 	if err = killProcessByPidFile(portReserverPidFile); err != nil {
 		log.L.WithError(err).Errorf("failed to kill the port-reserver process")
 	}
+	if err := os.RemoveAll(filepath.Dir(portReserverPidFile)); err != nil {
+		log.L.WithError(err).Errorf("failed to remove the port-reserver directory %s", filepath.Dir(portReserverPidFile))
+	}
 	return nil
 }