[cern] Fix docker-storage configuration

Cherry-pick from [1] for file:
magnum/drivers/common/templates/fragments/configure_docker_storage_driver_atomic.sh
Revert changes in:
magnum/drivers/common/templates/fragments/configure-docker-storage.sh
magnum/drivers/common/templates/fragments/configure-cvmfs.sh

Related-Ticket: OS-4106
[1] https://review.openstack.org/#/c/417457/