Code review comment for lp:~sergiusens/phablet-tools/recovery_from_system_images

Assuming this was tested, the code change looks good.

Note that in python3 python-tarfile supports opening xz-compressed files directly ("r:xz" mode) but I had reliability problems when doing that as part of the server work, so using lzma + uncompressed tarfile is probably safest at this point.