Use busybox dd

Tiny containers test consist in flashing a stable Apertis release and on
top of it download and test the tiny container of the release under test.
After switching the stable release to v2023.3 to support the new R-Car
board a failure is observerd due to missing dd.

In v2023, rust-coreutils is the replacement for coreutils, however, the
support of dd is disabled as it was still experimental and the replacement
chosen was busybox dd.

In order to fix the issue, switch to busybox dd to run the test.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

test-cases/tiny-container-user-device-sharing.yaml

@@ -32,7 +32,7 @@ run:
     - "# Ensure we have loop device:"
     - modprobe loop
     - "# Create the random file and map it to loop0 device on host:"
-    - dd if=/dev/urandom of=/var/test.img bs=1M count=1
+    - busybox dd if=/dev/urandom of=/var/test.img bs=1M count=1
     - losetup /dev/loop0 /var/test.img
     - "# Make sure user have correct mappings for test:"
     - usermod --add-subuids 1000-1000 user