setup-disk: fix partition failed on some machines

On some machines, sfdisk partition failed as 1M start offsets not aligns.

When set a aligned start offsets value. It works fine.

But it's recommended not to specify start offsets according to sfdisk manpage.

So this PR deprecated it.

https://man.archlinux.org/man/sfdisk.8.en#DESCRIPTION

The recommended way is not to specify start offsets at all and specify partition size in MiB, GiB (or so). In this case sfdisk aligns all partitions to block-device I/O limits (or when I/O limits are too small then to megabyte boundary to keep disk layout portable). If this default behaviour is unwanted (usually for very small partitions) then specify offsets and sizes in sectors. In this case sfdisk entirely follows specified numbers without any optimization.

---

Here is the case on scaleway Block volumes VM.

localhost:~# setup-disk -m sys /dev/sda
WARNING: The following disk(s) will be erased:
  sda   (10.0 GB SCW      b_ssd           )
WARNING: Erase the above disk(s) and continue? (y/n) [n] y
Sector 2048 already used.
Failed to add #1 partition: Result not representable

localhost:~# cfdisk /dev/sda
                                                               Disk: /dev/sda
                                            Size: 9.31 GiB, 10000000000 bytes, 19531250 sectors
                                        Label: gpt, identifier: B1472781-8E53-AA4F-AD26-45AEBE9AB83F

    Device                                 Start                    End                Sectors               Size Type
>>  Free space                              8192               19531216               19523025               9.3G

localhost:~# fdisk -l /dev/sda
Found valid GPT with protective MBR; using GPT

Disk /dev/sda: 19531250 sectors, 1344M
Logical sector size: 512
Disk identifier (GUID): b1472781-8e53-aa4f-ad26-45aebe9ab83f
Partition table holds up to 128 entries
First usable sector is 8192, last usable sector is 19531216

localhost:~# cat /sys/block/sda/queue/optimal_io_size
4194304