[Tails-dev] [review'n'merge:1.4] bugfix/8891-iso-image-paddi…

Hi,

please merge this branch into testing and devel, so that our ISO boots
on VirtualBox even in the cases when isohybrid makes it so its size is
not a multiple of 2048 bytes.

anonym: please note that I've added a few commits on top of your
original implementation, so that we get more info to report upstream
whenever we need.

Cheers,
--
intrigeri