cros_generate_update_payload: be clearer on what's being generated

BUG=None
TEST=Shows the payload type when starting/done.

Change-Id: I5ac5f10d28ff1bc7b9c894e546c5fadf90f898d4
Reviewed-on: https://chromium-review.googlesource.com/181223
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
1 file changed