Given the changes for multiple storage domains, do we want to allow a
user to specify multiple storage domains per disk when creating or
importing a template?
Otherwise the user will need to use the copy(clone) template disk
afterwards to create the copies of the storage domain disks where they
want them.
If so, what would the UI look for this? It would require the backend to
receive something that looks like Map<DiskImage, List<StorageDomain>>.
thoughts?