We're currently leaving around lots of empty directories in
/var/lib/docker/devicemapper/mnt/ for removed images and containers.
Fix this by removing the directory when the device is removed.
Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Upstream-commit: 2343fe44533f19ebae5e6127f4a2a19d1d8773fa
Component: engine