Use correct Env for DestroyDB in stress test (#6539)

Summary:
When using custom Env, trying to call DestroyDB() with default Options will
fail.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6539

Test Plan: ./db_stress

Differential Revision: D20476204

Pulled By: riversand963

fbshipit-source-id: 612c6754660cc9b5bb3e9c2dbb2f6ecd7f648797

db_stress_tool/db_stress_test_base.cc

@@ -41,6 +41,7 @@ StressTest::StressTest()
     }
 
     Options options;
+    options.env = db_stress_env;
     // Remove files without preserving manfiest files
 #ifndef ROCKSDB_LITE
     const Status s = !FLAGS_use_blob_db