In virDomainDefMaybeAddHostdevSCSIcontroller when we add a new
controller because someone neglected to add one or we're adding
one because the existing one is full, we should copy over the
model number from the existing controller since whatever we
create should at least have the same characteristics as the one
we cannot use because it's full.

NB: This affects the existing hostdev-scsi-autogen-address test
which would add a default ('lsi') SCSI controller for the various
scsi_host's that would create a controller for the hostdev.