Iterate over docker overlay mounts and umount them
Iterate over docker overlay mounts and umount them

This will occur after shutdown of docker daemon

[#156450862]

Signed-off-by: Brendan Nolan <e06848e0734297ec6ae611a089ce92cd4981b058@pivotal.io>
(cherry picked from commit 7efdba0a34c1c15f7d7e0ed05c68d800424e376a)

cf-platform-eng/docker-boshrelease,cloudfoundry-community/docker-boshrelease,cloudfoundry-community/docker-boshrelease,cf-platform-eng/docker-boshrelease