A small improvement in the SCSI request API.  Pass the status
at the time the request is completed, so that we can assert that
no request is completed twice.  This would have detected the
problem fixed in the previous patch.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>