This allows running reconfig during simulated stress test. Recommended
usage:

`$ USE_MOCK_CRYPTO=1 SIM_STRESS_TEST_DURATION_SECS=120
CHECKPOINTS_PER_EPOCH=30 cargo simtest test_simulated_load`

The `USE_MOCK_CRYPTO=1` is not necessary but makes the test run much
faster.

This immediately produces the following failure:

```
thread '<unnamed>' panicked at 'Older object version not found', /Users/mlogan/dev/sui/crates/sui-core/src/authority/authority_store.rs:1061:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

Other failures can likely be found with different seeds.