Comment 3 for bug 1632085

Motivating use case, also from Oli on the mailing list:

"""
on VMs the img file defines the "physical VM disk" while for an actual
install you write the img file to a pyhsical disk device ... the resize
code will find that the partition table does not cover all of the disk
before first boot and start the resize process so here the img size
wont be taken into account at all.

on a VM, all the resize code will see is the img file that pretends to
be a harddisk and it will find there is nothing to resize to.
"""

I plan on supporting this through a command line option that overrides the hardcoded 8MiB rootfs fudge factor.

For now, I won't change the 1.5x size calculation boost on all directory calculations, although this should certainly be addressed later.