New offset_increment option
This patch adds a new option to fio job files. It is described
in the HOWTO as follows:
offset_increment=int If this is provided, then the real offset becomes
the offset + offset_increment * thread_number, where the
thread number is a counter that starts at 0 and is incremented
for each job. This option is useful if there are several jobs
which are intended to operate on a file in parallel in disjoint
segments, with even spacing between the starting points.
Signed-off-by: Jens Axboe <axboe@kernel.dk>