The attribute disk_start_sector allows to specify a custom
start sector for the first partition of the disk. On GPT
tables everything works nicely, on DOS tables the used tools
fdisk/sfdisk are not able to manage the start/end values of
subsequent partitions if the first partition doesn't start
with the tooling default. This patch allows to set the
start sector after the partition table has been created
0540d6ddb9