Add support for VPD page b1 to scsi_debug

SCSI VPD page b1 reports the nominal rotation speed of the device.
Since scsi_debug is ram-based, claim to be a non-rotating medium.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Acked-by: Douglas Gilbert <dougg@torque.net>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>