Device handlers are optional, and for some handlers like ALUA only
implemented for certain device types.  So suppress any errors for
unsupported devices.
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>