chroot: let root be cleaned up by kernel
chroot: let root be cleaned up by kernel

Signed-off-by: Tonis Tiigi <c2470c48b2d3312d61f94f18d3a1cd113d1915ad@gmail.com>
(cherry picked from commit 70dfea63ba2a8a6d8b367420039aeb6a1759c240)
Signed-off-by: Victor Vieux <ce584ac70734cfa5a848cd28039798932c7ea675@docker.com>

medallia/docker,medallia/docker,medallia/docker,stainboy/docker,stainboy/docker,medallia/docker,stainboy/docker