add destroy thread for kill 15

src/storage/ob_table_store_stat_mgr.h

@@ -214,6 +214,8 @@ class ObTableStoreStatMgr
 {
 public:
   int init(const int64_t limit_cnt = DEFAULT_MAX_CNT);
+  void stop();
+  void wait();
   void destroy();
   static ObTableStoreStatMgr &get_instance();
   int report_stat(const ObTableStoreStat &stat);