- allow QEMU name to have subdirectory inside (replace `/` by `__` in
the filename)
- add a new code path for plain qcow2 image (for efficient bandwidth
usage, the qcow2 is expected to use compressed qcow2 format)
- move freebsd image to explicitly download the gzipped QEMU
Previously we were somewhat half-Docker, half-Travis, half apt-get, etc. This
commit alters the CI infrastructure to use Docker images for each target. This
should make it much easier to update the images and tweak various bits and
pieces of installed software. Additionally, it's also much clearer now what's
needed for each suite of tests!
Some images were updated a bit (e.g. musl is now 1.1.14), but other images
encountered failures when updating so they're not getting updated just yet.
