If provided, round the disk image size up to a multiple of the value.
This allows for image formats with specific size-alignment requirements
(e.g., disk size must be in GiB).
(cherry picked from commit 8ef4f431d8)
reqpart can be used to make kickstarts more platform agnostic, creating
needed partitions without lmc having to keep track of the arch-specific
needs. eg. ppc64 needs prepboot and /boot
This increases the size of the disk based on whether reqpart or
reqpart --add-boot is in the kickstart.
Note that this is only valid for partitioned disk output types, not
for filesystem images or live iso output.
