Add iterator refresh to stress test (#10766)

Summary:
added calls to `Iterator::Refresh()` in `NonBatchedOpsStressTest::TestIterateAgainstExpected()`. The testing key range is locked in `TestIterateAgainstExpected` so I do not expect this change to provide thorough stress test to `Iterator::Refresh()`. However, it can still be helpful for catching bugs like https://github.com/facebook/rocksdb/issues/10739. Will add calls to refresh in `TestIterate` once we support iterator refresh with snapshots.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10766

Test Plan: `python3 tools/db_crashtest.py whitebox --simple --verify_iterator_with_expected_state_one_in=2`

Reviewed By: ajkr

Differential Revision: D40008320

Pulled By: ajkr

fbshipit-source-id: cec93b07f915ef6476d41c1fee9b23c115188085

db_stress_tool/no_batched_ops_stress.cc

@@ -1224,6 +1224,11 @@ class NonBatchedOpsStressTest : public StressTest {
       op_logs += "P";
     }
 
+    if (thread->rand.OneIn(2)) {
+      // Refresh after forward/backward scan to allow higher chance of SV
+      // change. It is safe to refresh since the testing key range is locked.
+      iter->Refresh();
+    }
     // start from middle of [lb, ub) otherwise it is easy to iterate out of
     // locked range
     int64_t mid = lb + static_cast<int64_t>(FLAGS_num_iterations / 2);