scsi: virtio_scsi: let host do exception handling

scsi: virtio_scsi: let host do exception handling

virtio_scsi tries to do exception handling after the default 30 seconds
timeout expires.  However, it's better to let the host control the
timeout, otherwise with a heavy I/O load it is likely that an abort will
also timeout.  This leads to fatal errors like filesystems going
offline.

Disable the 'sd' timeout and allow the host to do exception handling,
following the precedent of the storvsc driver.

Hannes has a proposal to introduce timeouts in virtio, but this provides
an immediate solution for stable kernels too.

[mkp: fixed typo]

Reported-by: Douglas Miller <dougmill@linux.vnet.ibm.com>
Cc: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: linux-scsi@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Orabug: 28856913

(cherry picked from commit e72c9a2a67a6400c8ef3d01d4c461dbbbfa0e1f0)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
- The function above virtscsi_host_template_single() is
  virtscsi_target_destroy() (in uek4), but not virtscsi_map_queues() (in
  upstream)
- virtscsi_host_template_multi.slave_alloc is implemented in upstream, but
  not uek4

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Patrick Colp <patrick.colp@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>