Only allow one storage device when using/creating LXD pods

[Caleb-Ellis]

MAAS libvirt Pods allow users to specify how many virtual disks, at what size, you want for libvirt composed machines. Our goal with LXD Pods is feature parity with libvirt. Newell and I were unable to figure out how to add multiple disks to a VM with LXD and asked Stéphane for help. Unfortunately LXD does not have an API available to create additional virtual disks for a VM. We can specify the size for that block device but can't add more. Stéphane indicated adding support for multiple virtual block devices would be a larger task for LXD. Should we ask LXD to add this feature or ask design to disallow having more than one disk for LXD Pods?

Disallow for now, we can't wait for LXD to add this.

Only one storage is allowed but you can dictate the size and the pool.

Zeplin wireframe