lxd/storage/backend/lxd: Delete any left over image volumes in Delete
lxd/storage/backend/lxd: Delete any left over image volumes in Delete

Avoids blocking the storage pool from being deleted if orphaned image volumes are left after a storage pool recovery.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

hallyn/lxd,lxc/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,atxwebs/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,atxwebs/lxd