scsi: core: add scsi_host_complete_all_commands() helper

Add a helper scsi_host_complete_all_commands() to terminate all outstanding
commands on a SCSI host.

Link: https://lore.kernel.org/r/20200228075318.91255-3-hare@suse.de


Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>