Improve switchover undo when new master fails

Now the monitor properly restores the old master by running promotion code on it.
Also, binlog is disabled when enabling server events.

server/modules/monitor/mariadbmon/server_utils.hh

@@ -222,7 +222,8 @@ using EventNameSet = std::unordered_set<std::string>;
 enum class OperationType
 {
     SWITCHOVER,
-    FAILOVER
+    FAILOVER,
+    UNDO_DEMOTION // Performed when switchover fails in its first stages.
 };
 
 class GeneralOpData