fix:(disk_setup):handle empty disk in check_partition_gpt_layout_sfdisk

[xiachen-rh]

When checking GPT partition layout using sfdisk, handle the case where a disk has no partition table yet.
Previously, it would raise an exception.
Because check_partition_gpt_layout_sfdisk calls "sfdisk -l -J ", the command exits with code 1 and the error "does not contain a recognized partition table". The code doesn't handle it and raises an error.
Now it returns an empty list.
I also add unit test to cover this empty disk scenario.

Fixes GH-6682

Test Steps

I run test on OpenStack with an additional empty disk with config data as below

# cat /etc/cloud/cloud.cfg.d/disk.cfg 
#cloud-config
disk_setup:
  /dev/vdb:
    table_type: 'gpt'
    layout: True
    overwrite: True

steps

1. Create a volume and attach it to a instance
2. login, and prepare configuration data for cloud-init to do disk setup
3. clean cloud-init and reboot
4. check the result

After fix, no unexpected error about sfdisk, and the additional disk /dev/vdb is parted

# lsblk 
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
vda    252:0    0   20G  0 disk 
├─vda1 252:1    0    1M  0 part 
├─vda2 252:2    0  200M  0 part /boot/efi
└─vda3 252:3    0 19.8G  0 part /
vdb    252:16   0   50G  0 disk 
└─vdb1 252:17   0   50G  0 part 

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)