Fix the issue that user can't add alerts.
Fix the issue that user can't add alerts.

When seeded from the fixture file, default events in miq_event_definitions table always belong to certain event set.
However there are some appliances from 5.6 fresh installation that have some deleted old events showed up in the DB and not belong to any event set.
UI for Add a New Alert would not open due to these ghost and orphaned events.

So far we can't find out why these deleted events still showed up in a fresh appliance. It is strange.
This commit would skip these orphaned events so users can access the Add a New Alert page.

https://bugzilla.redhat.com/show_bug.cgi?id=1379854
(transferred from ManageIQ/manageiq@2e1953182187be58268b7ab88d18a66692a886fa)

ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic