LU-2100 ofd: small batched precreation on a small system

LU-2100 ofd: small batched precreation on a small system

on a small system (like NAME=local configuration) ldiskfs
transactions can not accept many changes. with batched
precreation in OFD, the default value of 128 objects may
lead to warnings and transaction overflow. to prevent this
OFD checks fs and if it's small (OFD_PRECREATE_SMALL_FS
= 1GB), then initial number of objects to precreate in a
single transaction is set to OFD_PRECREATE_BATCH_SMALL=8.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: Id9b9c4b6abd76df69787777cc52380d71fdf5a86
Reviewed-on: http://review.whamcloud.com/4274
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>