ci-automation: align VM image compression with existing pipeline

In jenkins/vms.sh the Digital Ocean and OpenStack images get also
compressed as gzip.
Do so for the new pipeline, too.

ci-automation/vms.sh

@@ -105,10 +105,15 @@ function _vm_build_impl() {
 
     for format in ${formats}; do
         echo " ###################  VENDOR '${format}' ################### "
+        COMPRESSION_FORMAT="bz2"
+        if [[ "${format}" =~ ^(openstack|openstack_mini|digitalocean)$ ]];then
+            COMPRESSION_FORMAT="gz,bz2"
+        fi
         ./run_sdk_container -n "${vms_container}" -C "${image_image}" \
             -v "${vernum}" \
             ./image_to_vm.sh --format "${format}" --board="${arch}-usr" \
-                --from "${CONTAINER_IMAGE_ROOT}/${arch}-usr/latest"
+                --from "${CONTAINER_IMAGE_ROOT}/${arch}-usr/latest" \
+                --image_compression_formats="${COMPRESSION_FORMAT}"
     done
 
     # copy resulting images + push to buildcache