LU-2302 scripts: prevent lfs_migrate data disclosure

LU-2302 scripts: prevent lfs_migrate data disclosure

Tighten umask to make sure temporary rsync files are created
with strict permissions that don't grant access to unprivileged
users.

Signed-off-by: Daniel Kobras <d.kobras@science-computing.de>
Change-Id: Ie662edfd615a24ce08cbddb9347f197de41d4d27
Reviewed-on: http://review.whamcloud.com/4699
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>