This adds support for virtio-scsi on KVM hosts, either
for guests that are associated with a new os_type of 'Other PV Virtio-SCSI (64-bit)',
or when a VM or template is regstered with a detail parameter rootDiskController=scsi.
Update cloudstack add template dialog to allow for selecting rootDiskController with KVM
Update cloudstack kvm virtio-scsi to enable discard=unmap