eta: improve accuracy for rwmix workloads and verify

We assume 50/50 for mixed workloads. That's silly, use the actual
number specified instead.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Ensure all random seeds are repeatable for randrepeat=1

Currently we only do the offset.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Make experimental_verify=1 handle all cases properly

- Don't track written bytes, just replay the workload by resetting
  all the random generators. This should work for any mixture of IO.

- Handle trims for verify.

- Ensure that rwmix is replayed properly for verify.

- Fixup logging for replay.

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