imsm: monitor: do not finish migration if there are no failed disks

imsm: monitor: do not finish migration if there are no failed disks

Transition from "degraded" to "recovery" made in OROM is slightly different
than the same transision in mdadm. Missing disk is not removed from list of
raid devices, but just from map. Therefore mdadm should not end migration
basing on existence of list of missing disks but should rely on count of
failed disks.

Signed-off-by: Przemyslaw Czarnowski <przemyslaw.hawrylewicz.czarnowski@intel.com>
Tested-by: Pawel Baldysiak <pawel.baldysiak@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>