LU-11681 lfsck: misc fixes for dangling entry repair

LU-11681 lfsck: misc fixes for dangling entry repair

* lock child in dangling entry repair.
* if child is directory, create it as plain directory, because
  it may have shards already, which will be inserted later, besides,
  it may be remote, and creating striped directory remotely is not
  supported.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: Ide0d90f99e6d24f4a9507d98bbc7ad7f876a907d
Reviewed-on: https://review.whamcloud.com/33927
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>