Fix a bug in tests in options operator=

Summary:
Note: Using the default operator= is an unsafe approach for Options since it destructs shared_ptr in
the same order of their creation, in contrast to destructors which
destructs them in the opposite order of creation. One particular problme is
that the cache destructor might invoke callback functions that use Option
members such as statistics. To work around this problem, we manually call
destructor of table_facotry which eventually clears the block cache.
Closes https://github.com/facebook/rocksdb/pull/1950

Differential Revision: D4655473

Pulled By: maysamyabandeh

fbshipit-source-id: 6c4bbff

db/db_test_util.cc

@@ -511,6 +511,13 @@ Status DBTestBase::ReadOnlyReopen(const Options& options) {
 
 Status DBTestBase::TryReopen(const Options& options) {
   Close();
+  last_options_.table_factory.reset();
+  // Note: operator= is an unsafe approach here since it destructs shared_ptr in
+  // the same order of their creation, in contrast to destructors which
+  // destructs them in the opposite order of creation. One particular problme is
+  // that the cache destructor might invoke callback functions that use Option
+  // members such as statistics. To work around this problem, we manually call
+  // destructor of table_facotry which eventually clears the block cache.
   last_options_ = options;
   return DB::Open(options, dbname_, &db_);
 }