cciss: make rebuild_lun_table behave better

This patch makes the rebuild_lun_table smart enough to not rip a logical
volume out from under the OS. Without this fix if a customer is running
hpacucli to monitor their storage the driver will blindly remove and re-add
the disks whenever the utility calls the CCISS_REGNEWD ioctl. Unfortunately,
both hpacucli and ACUXE call the ioctl repeatedly. Customers have reported
IO coming to a standstill. Calling the ioctl is the problem, this patch is
the fix.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cca.cpqcorp.net>
Signed-off-by: Mike Miller <mike.miller@hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>