conf: Store SCSI bus length in virDomainDef

conf: Store SCSI bus length in virDomainDef

Libvirt assumes that a SCSI bus can fit up to 8 devices
(including controller itself), except for so called wide bus
which can accommodate up to 16 devices (again, including
controller). This plays important role when computing 'drive'
address in virDomainDiskDefAssignAddress(). So far, the only
driver that enables wide SCSI bus is VMX. But with newer
releases, ESX is capable of "super wide" bus (64 devices).

We can blindly bump the limit in our code because then we would
compute address that's invalid for older ESX versions that we
still want to support.

Unfortunately, I haven't found a better place where to store this
than virDomainDef.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>