Ubuntu cloud image partition numbering

Hi,

When downloading an image (e.g. noble) from https://cloud-images.ubuntu.com/ and unpacking it onto a disk (using `qemu-img`), we see that the partition numbering starts at 1, skips number 2-13 and continues with 14:

sda 8:0 0 10G 0 disk
├─sda1 8:1 0 9G 0 part /
├─sda14 8:14 0 4M 0 part
├─sda15 8:15 0 106M 0 part /boot/efi
└─sda16 259:0 0 913M 0 part /boot

This hits a limitation in Dell's PowerFlex SDC (storage) when trying to launch Ubuntu noble based VMs backed by PowerFlex disks.
We have experienced this recently in the LXD team whilst adding support for SDC in our LXD PowerFlex storage driver.

Dell supports at max 15 partitions on their disks, see https://www.dell.com/support/manuals/en-us/scaleio/flex-software-to-46x/product-limits?guid=guid-a8f27cd4-d5f7-4993-93ea-0a739256633d&lang=en-us:

> Maximum file system partitions per volume: 15

This wasn't an issue before as the maximum partition number in the jammy image is 15.

In order to resolve this issue a proposal could be changing the partition numbers to start at 13 so that we still stay in the limit of 15.