Code review comment for lp://staging/~barry/ubuntu-system-image/test-fixes

What does this mean, that python 2.7 "does not have" tar.xz files? We are using python2.7 in production, and we must support tar.xz in production (both as an import source and as a generation target). If the test as written can't test tar.xz support correctly on python2.7, then the test should be fixed, not skipped.