Slightly adjust atomic white box test's kill odd (#5717)

Summary:
Atomic white box test's kill odd is the same as normal test. However, in the scenario that only WritableFileWriter::Append() is blacklisted, WritableFileWriter::Flush() dominates the killing odds. Normally, most of WritableFileWriter::Flush() are called in WAL writes, where every write triggers a WAL flush. In atomic test, WAL is disabled, so the kill happens less frequently than we antipated. In some rare cases, the kill didn't end up with happening (for reasons I still don't fully understand) and cause the stress test timeout.

If WAL is disabled, make the odds 5x likely to trigger.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5717

Test Plan: Run whitebox_crash_test_with_atomic_flush and whitebox_crash_test and observe the kill odds printed out.

Differential Revision: D16897237

fbshipit-source-id: cbf5d96f6fc0e980523d0f1f94bf4e72cdb82d1c

tools/db_crashtest.py

@@ -288,8 +288,12 @@ def whitebox_crash_main(args, unknown_args):
                     "kill_random_test": kill_random_test,
                 })
             elif kill_mode == 1:
+                if cmd_params.get('disable_wal', 0) == 1:
+                    my_kill_odd = kill_random_test / 50 + 1
+                else:
+                    my_kill_odd = kill_random_test / 10 + 1
                 additional_opts.update({
-                    "kill_random_test": (kill_random_test / 10 + 1),
+                    "kill_random_test": my_kill_odd,
                     "kill_prefix_blacklist": "WritableFileWriter::Append,"
                     + "WritableFileWriter::WriteBuffered",
                 })