mounted memoryfs doesn't show on GUI

[XiaochenCui]

the mounted memoryfs doesn't show on it's parent /admin, which is not the case when this feature just finished.

    "mountpoint": {
      "mountpoints": {
        "/": {
          "mounter": "puterfs"
        },
        "/admin/tmp": {
          "mounter": "memoryfs"
        }
      }
    }

It would be great if this can be guarded by a test