lxd/storage/drivers/zfs/volumes: Makes MountVolume and UnmountVolume more thorough in detecting mounts
lxd/storage/drivers/zfs/volumes: Makes MountVolume and UnmountVolume more thorough in detecting mounts

Improves debug logging too.

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

Skarlso/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,Skarlso/lxd,mjeanson/lxd,Skarlso/lxd,mjeanson/lxd,hallyn/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,mjeanson/lxd,Skarlso/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,atxwebs/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd