LU-7712 mdd: migration is too noisy

LU-7712 mdd: migration is too noisy

even in the normal cases when we can't migrate a file due to
activity on it or missing file, etc.

Change-Id: Iee320963116cbb5a141bbeb358eb8f604aa6a533
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: http://review.whamcloud.com/18145
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>