fix(cgpt.py): Fix GPT reserved space calculations.

The existing code arbitrarily multiplies START_SECTOR by 512 converting
from blocks/sectors to bytes, but blocks was the correct unit to begin
with. Also the secondary GPT area is not considered but that was OK
because the bogus unit conversion oversized our disks by almost 16MB.

Instead of relying on bugs properly reserve 34 sectors at each end of
the disk. (Well, we could get away with only 33 at the end since it
doesn't have a MBR but meh.)
fix(cgpt.py): Add support for aligning partitions

When using anything other than classic spinning disks with 512 sectors
it is generally best to maintain some alignment with the underlying
physical sector or erase block size. The default alignment most
partitioning tools use these days is 1MB (2048 sectors). Also sometimes
qemu-img requires disk sizes to be aligned to 64KB.
fix(legacy_disk_layout.json): Omit unused partitions.

We don't need to reserve space on disk just to reserve partition
numbers. And now that partitions are aligned these blanks spots grew
from 512 bytes to 1MB which is not much but still silly.
Merge pull request #123 from marineam/align

Align partitions