kata-deploy: tools: tests: Use zstd instead of xz

Although the compress ratio is not as optimal as using xz, it's way
faster to compress / uncompress, and it's "good enough".

This change is not small, but it's still self-contained, and has to get
in at once, in order to help bisects in the future.

Signed-off-by: Fabiano Fidêncio <fabiano@fidencio.org>

tools/osbuilder/rootfs-builder/debian/Dockerfile.in

@@ -33,7 +33,8 @@ RUN apt-get update && apt-get --no-install-recommends install -y \
     tar \
     vim \
     wget \
-    xz-utils
+    xz-utils \
+    zstd
 # aarch64 requires this name -- link for all
 RUN ln -s /usr/bin/musl-gcc "/usr/bin/$(uname -m)-linux-musl-gcc"