[Libguestfs] [PATCH] Fix make-fedora-img for btrfs minimum size

[Mike Kelly]

This first factors out all the partition sizing, and then resizes the
images created to be 1GB instead of 512MB, to work around a size
limitation with btrfs:

  mkfs_btrfs: /dev/vda2: device /dev/vda2 is too small (must be at least
  256 MB)