LU-14719 utils: dir migration stop on error

LU-14719 utils: dir migration stop on error

Once directory migration fails, it should stop immediately since
current migration won't succceed, and subsequent migration may
fail on the same error.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I96c1693d1b1da0856c925b9b22c1ab7f3181f0d8
Reviewed-on: https://review.whamcloud.com/47040
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>