dedupe: read in larger chunks at the time

Signed-off-by: Jens Axboe <axboe@fb.com>
Add ability to use an include file in a fio job file

With this patch, we can use the 'include' directive to tell
fio to include the contents of a file inside a job file.

Signed-off-by: Jens Axboe <axboe@fb.com>