kvmrbdfio ignores time_based from YAML

Currently, librbdfio honors `time_based: True` from the benchmark YAML and passes `--time_based` to fio.

kvmrbdfio does not. It always passes `--runtime=` and `--size=`, and it only adds `--time_based` when `recovery_test` is set.

Without `--time_based`, fio treats `--runtime` as a maximum. The job still stops when `--size=` is filled. Sequential write/read of a modest image can finish in a few seconds even when YAML asked for a any seconds sample.

That makes `librbdfio` vs `kvmrbdfio` comparisons with the same `time` / `time_based` YAML invalid: one path ran for the full window, the other may not have.

Even with:

```yaml
benchmarks:
kvmrbdfio:
time: 60
time_based: True
```

fio should run for 60 seconds (--runtime=60 --time_based), same as librbdfio, I personally faced this a benchmarking limitation while running cbt for my own ceph cluster.

Start by locating the kvmrbdfio entry point that converts benchmark YAML into fio arguments, then compare its handling of time_based with librbdfio. Verify the YAML example produces --runtime=60 together with --time_based, and confirm the benchmark runs for the requested time window.

Written by the indexing model from the issue text.