imsm: FIX: Clear migration record when migration switches to next volume.
When OLCE is in progress, checkpoint steps are getting bigger due to added space during process.
When mdadm fails after saving "max" to sync_max, mdmon will monitor process
and switch reshape to next array. At this moment we have got information
inconsistency between metadata and migration record.
To avoid this, clear migration record by mdmon /exception from the rule
that migration record is maintained by mdadm/ when reshape switches
to next array.
Signed-off-by: Adam Kwolek <adam.kwolek@intel.com> Signed-off-by: NeilBrown <neilb@suse.de>