Add sample zipf distribution randomizer

Instead of just doing purely random IO where each block is
touched exactly (or close to, depending on random map) once,
add a zipf distribution scheme where a selectable theta
defines the spread and frequency of blocks read/written.

Committing this so I don't lose it. Needs a few changes,
for instance we need to hash the zipf output so that
the spread doesn't always just favor the lower LBA range.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
10 files changed