UUID of ext4 volumes generated by make_ext4fs are determined by volume
label and it will all be 57f8f4bc-abf4-655f-bf67-946fc0f9f25b when label
is empty

Labeling them does not make them unique but tools like block command
from fstools have a better chance differentiating them

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>