Work backwards for known units
Work backwards for known units

Signed-off-by: Chuck Short <753a8074f04ffd62a8fff7516e3ae689be8e35ad@canonical.com>

Saviq/nova-compute-lxd,tpouyer/nova-lxd,Saviq/nova-compute-lxd,tpouyer/nova-lxd,mmasaki/nova-compute-lxd,mmasaki/nova-compute-lxd