On Windows, the .bz2 compression format is not supported by native
tooling and external tools like 7zip need to be installed.
Switching to .zip compression, there will be no need for the extra step
of having external tools.
See: https://github.com/flatcar/Flatcar/issues/1009
Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>
