In recent versions of OpenNMS, the eventdpname is always set to 'localhost' to match the default value in the distpoller table. However, events that occurred before this update will have 'undefined' or 'localhost', depending on which subsystem created the event.

We need to create a Liquibase migration that updates the value of the column to match the default value that represents the local OpenNMS machine so that all events are associated with that system.