fix(cgpt): Drop O_NOFOLLOW flag from open()

It is unclear why O_NOFOLLOW was added other than a very vague note in
commit c4e92af8. The bug it references is unavailable. The flag breaks
referring to devices via any of the oodles of symlinks in /dev.
fix(cgpt): Add support for repairing resized disks.

As-is `cgpt repair` when confronted with a disk with a new size will
write the existing table with the old sizes, leaving the disk every bit
as broken as it was before. Now in addition to replacing the secondary
header it will properly recompute the properties that depend on disk
size and update both headers.