scsi_debug: Add support for physical block exponent and alignment

This patch adds support for setting the physical block exponent and
lowest aligned LBA in the READ CAPACITY(16) response.

The B0 VPD page is adjusted accordingly.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>