Fukász Rómeó Ervin / cloud

⚠ Requires support in circle/storagedriver (at least
storagedriver/94379fb).

✅ add InstanceTemplate.save_as/_async
✅ #24 create disk from iso url
✅ add Disk.create (replace all Disk.objects.create and
Disk.__init__ calls)
✅ add Disk.create_empty