LU-2302 scripts: null-terminated file lists in lfs_migrate

LU-2302 scripts: null-terminated file lists in lfs_migrate

New option -0 allows to use a null-terminated list of file names
on stdin. Changed internal lfs find to use null-terminates lists.

Signed-off-by: Daniel Kobras <d.kobras@science-computing.de>
Change-Id: Iccd928a766968a7513833035684d41a1060c4a4d
Reviewed-on: http://review.whamcloud.com/4700
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>