Merge branch 'qemu-img' into 'master'

ci: use qemu-img to convert and compress rootfs

See merge request !14

.gitlab-ci.yml

@@ -9,7 +9,7 @@ include: "https://git.autistici.org/pipelines/debian/raw/master/common.yml"
     - env http_proxy=${APT_PROXY:+http://${APT_PROXY}} autopkgtest-build-qemu --size 10G $DIST build-$CI_JOB_ID/rootfs.img http://deb.debian.org/debian amd64 $PWD/aux/post-install.sh
     - ./aux/extract-kernel.sh build-$CI_JOB_ID/rootfs.img build-$CI_JOB_ID/
     - mv build-$CI_JOB_ID/rootfs.img build-$CI_JOB_ID/rootfs.img.orig
-    - env TMPDIR=$PWD virt-sparsify --compress build-$CI_JOB_ID/rootfs.img.orig build-$CI_JOB_ID/rootfs.img
+    - qemu-img convert -c build-$CI_JOB_ID/rootfs.img.orig -O qcow2 build-$CI_JOB_ID/rootfs.img
     - rm build-$CI_JOB_ID/rootfs.img.orig
     - tar -c -f $DIST-$CI_JOB_ID.tar -C build-$CI_JOB_ID .
     - ls -l $DIST-$CI_JOB_ID.tar