Reverse search order for ide disks for cloud-init allocation.

[jeff-voight]

Reverses the order of the cloud-init ide drive selection to start at low numbers instead of starting at high numbers.

This solves an issue where when building an image with cloud-init enabled, proxmox reports the following:

generating cloud-init ISO
kvm: -device ide-cd,bus=ide.1,unit=1,drive=drive-ide3,id=ide3: Can't create IDE unit 1, bus supports only 1 units
TASK ERROR: start failed: QEMU exited with code 1

Closes Plugin assigns bad ide drive to cloud-init #55

Can be tested by cloning: https://github.com/VoightCloud/CopperCentos7.git

Modify username to your proxmox packer username, modify token to your proxmox token, modify node to your node, modify proxmox_url to your proxmox_url, upload Centos-7-x86_64-Everything-2009.iso to your local:iso/ storage.

cd into packer directory and type ./build.sh

[hashicorp-cla]

All committers have signed the CLA.

[jeff-voight]

I think the ci/circleci tests may have to re-run. I saw failures that lead me to believe that something else is stuck in the pipeline that's affecting my build.

[azr]

cc @carlpett 🙂

[carlpett]

Change itself looks fine, thanks! The context around has quite odd indentation though, could you check if it is gofmt:ed? (Could just be Github acting up)

[azr]

+1, also, the TestTemplateFinalize/all_options_with_cloud-init test seems to fail.

[azr]

LGTM !