LXC TurrisOS rootfs does not look like a tar archive
https://api.turris.cz/lxc/images/Turris_OS/stable/armv7l/2016-12-25/rootfs.tar.xz is malformed. Because of that it's not possible to create TurrisOS LXC container.
More info: https://forum.turris.cz/t/cant-create-turris-stable-lxc/2531/4