Pass the correct comparator to MultiScanArgs (facebook#14033)

Summary:
Fix assertion failure in crash tests with timestamp due to the wrong comparator passed to MultiScanArgs

Pull Request resolved: facebook#14033

Reviewed By: xingbowang

Differential Revision: D84036954

Pulled By: anand1976

fbshipit-source-id: 526be21c0754dcccf8e4d2b9fba33716fe35860a

Author: anand1976

db_stress_tool/db_stress_test_base.cc

@@ -1694,7 +1694,7 @@ Status StressTest::TestMultiScan(ThreadState* thread,
   std::vector<std::string> start_key_strs;
   std::vector<std::string> end_key_strs;
   // TODO support reverse BytewiseComparator in the stress test
-  MultiScanArgs scan_opts(BytewiseComparator());
+  MultiScanArgs scan_opts(options_.comparator);
   scan_opts.use_async_io = FLAGS_multiscan_use_async_io;
   start_key_strs.reserve(num_scans);
   end_key_strs.reserve(num_scans);