Partitions by default are indexed starting at 1, but in
some cases, such as CoreOS for IBM Z, it may be usefull
to set the 'partnum' for GPT disks explicitly, without
creating dummy partitions.
Now user can define an image:
```
mpp-define-images:
- id: image
size: 10737418240
table:
uuid: 00000000-0000-4000-a000-000000000001
label: gpt
partitions:
- name: boot
type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
partnum: 3
size: 786432
- name: root
type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
partnum: 4
size: 4194304
```
So target disk would look like:
```
Disklabel type: gpt
Disk identifier: 00000000-0000-4000-A000-000000000001
Device Start End Sectors Size Type
/dev/loop0p3 2048 788479 786432 384M Linux filesystem
/dev/loop0p4 788480 4982783 4194304 2G Linux filesystem
```
This patch updates the osbuild-mpp tool and the sgdisk and sfdisk
stages to support this.
Co-authored-by: Dusty Mabe <dusty@dustymabe.com>
fc185dae8c