Closes #8356: Add virtual disk to Virtual Machines

[arthanson]

Fixes: #8356

introduces a new VirtualDisk model with name and size fields, instances of which must be assigned to a specific virtual machine. Retains the existing disk field on VirtualMachine.

Switched Virtual Machine list view to show Disk Size (from Virtual Disks) instead of Disk - made it default, but user can add disks back if needed. I think this makes it very clear that they should be moved.

Also put in deprecation warnings for Disk in detail / edit view:

Added Virtual Disks to end of Virtual Machine detail view:

[ITJamie]

Can i suggest that we add config context to the new VirtualDisk model.
this would be useful for documenting disk type information (disk io settings, adaptor type, disk position ids, storage location info etc).

[jeremystretch]

Great work, @arthanson! Just have some minor cleanup notes.

Also, we should consider how best to report disk space for a VM given the presence of both VirtualDisks and the disk field on VirtualMachine. E.g. it might make sense to introduce a total_disk_size property on VirtualMachine.

[amhn]

Just a minor note:
Using the GUI the URL component is named "disks" (e.g. http://localhost:8000/virtualization/disks/1/) while in the API it is named "virtual-disks" (e.g. http://localhost:8000/api/virtualization/virtual-disks/1/). Probably should be the same in both.

[jeremystretch]

I'm going to take a stab at annotating the disk size on VM querysets.