lxd/device/disk: Ensure that host-side device mounts are cleaned up in postStop
lxd/device/disk: Ensure that host-side device mounts are cleaned up in postStop

This is now done even if the pool volume has been unmounted because this is not done on start for VMs.

Also change order of cleanup so that bind mount in devices dir is cleaned up first, before the pool volume mount (as that depends on the other).

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

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