Fix for devices with a non-512-byte sector size

[mmstick]

This will require testing with disks with non-512 byte sector sizes. I don't think we sell any of these.
There will be an accompanying installer PR to test this within a few minutes.

Closes #177

[jackpot51]

Is it possible to emulate a 4096 byte sector device, in QEMU for example?

[mmstick]

That does seem to be possible. After creating a VM with virt-manager, and changing the disk from IDE to VirtIO, then opening the VM XML config for editing with virsh edit ${vm_name}, adding <blockio logical_block_size='4096' physical_block_size='4096'/> to the <disk> section will set the disk to emulate 4K logical sector sizes.

[jackpot51]

Ok, please get @brs17 up and going with that setup

[mmstick]

Found some issues. Will notify when this is ready for testing.

[mmstick]

It seems to be working with 512 and 4096 byte logical block sizes. The installs succeed and the partitions report the correct sizes during configuration and after install. However, I have yet to figure out how to get the VM to boot from a 4096-sized VirtIO device. The EFI doesn't seem to be detecting systemd-boot.

[vjr]

@mmstick what was the reason this PR was closed without review/merge? I've mostly taken this code into my PR #278 which I've marked ready for review.