qemuBuildHostdevSCSI(A|De)tachPrepare: Use virStorageSource in def for SCSI hostdevs
Modify the attach/detach data generators to actually use the
virStorageSourceStructure embedded in the SCSI config data rather than
creating an ad-hoc internal one.
The modification will allow us to properly store the nodename used for
the backend in the status XML rather than re-generating it all the
time.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>