infra: Remove temp files after update_iso

The `makeupdates` script was executed with `-k` parameter which will
keep `updates` directory after the image is created. In the end it means
that next updates image created will contain all the files from previous
creation.

It wasn't such an issue before rpm unpack was implemented but now it's
causing a mess.

scripts/testing/update_iso

@@ -88,7 +88,7 @@ def make_updates_image(git_id, rpm_paths):
  # Create the necessary folder structure
  os.makedirs(UPDATES_FOLDER, exist_ok=True)
  # Prepare updates image
- cmd = f"./scripts/makeupdates -k -c -t {git_id}{rpm_args}"
+ cmd = f"./scripts/makeupdates -c -t {git_id}{rpm_args}"
  print("** Calling:", cmd)
  os.system(cmd)
  # Move it next to the ISOs