Show correct mbr zip file size
Show correct mbr zip file size

(cherry picked from commit 39e7ee3a1903647ddc4fbcf353ee2059e68d318b)
(cherry picked from commit 9e1dd64ac673db4fa906d2219816510507c284de)

uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend