scsi: Update sense code handling

The SCSI spec has a quite detailed list of sense codes available.
It even mandates the use of specific ones for some failure cases.
The current implementation just has one type of generic error
which is actually a violation of the spec in certain cases.
This patch introduces various predefined sense codes to have the
sense code reporting more in line with the spec.

On top of Hannes's patch I fixed the reply to REQUEST SENSE commands
with DESC=0 and a small (<18) length.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
