MDEV-31463 Spider should check connection before setting lock wait timeout

When setting the server lockwait timeout, spider should do some basic
checks first, like whether the remote server is still reachable. So
instead of directly calling spider_db_mbase::exec_query(), it should
call spider_db_query().

The reset of the lock wait timeout does not need to do such checks,
because they happen after the successfully setting the lock wait
timeout, implying the checks have been passed already.

storage/spider/spd_db_mysql.h

@@ -514,8 +514,6 @@ public:
     int *need_mon
   );
 
-  /** Set the global lock wait time out */
-  int set_lock_wait_timeout(uint timeout);
   /** Reset the global lock wait time out */
   int reset_lock_wait_timeout();