Root device partitioning now aligns to 1MiB

- partition sizes are still calculated the same way
- rounds up each partition to the next 1MiB to improve performance
- truncates the last requested partition if it exceeds the size of the disk
- 1MiB was selected for optimal performance on HDD or SSD (at the
  cost of a little disk space between partitions)
- should prevent parted from refusing to partition or warn of
  sub-optimal alignment

[#83141758]
Fixed off-by-one error

- root partition end positions will now be odd instead of even
- no space will be left between the swap and ephemeral partitions

[#83141758]