file: add bloom filter to avoid quadratic lookup behavior

file: add bloom filter to avoid quadratic lookup behavior

If we have a lot of jobs, with a lot of subjobs, and they each
have a lot of files, we get pathetic startup performance
because each file add will check all the previously added
files.

Fixes: bcbfeefa7bce ("fio: add multi directory support")
Signed-off-by: Jens Axboe <axboe@fb.com>