Switchover fails if event scheduler is disabled in server configuration

Disabling the entire event scheduler in server configuration (event_scheduler=DISABLED) disables the entire information_schema.EVENTS-table, causing a select-query against it to fail. This then fails the cluster operation (e.g. switchover). This issue can be bypassed by configuring the monitor with handle_events=false. Still, the monitor should detect this case and skip event manipulation.