Exclude specific events.

Exclude Host/VM C&U Processing Events from Policy Event assignments screen.

https://bugzilla.redhat.com/show_bug.cgi?id=1012619
https://bugzilla.redhat.com/show_bug.cgi?id=1155244
https://bugzilla.redhat.com/show_bug.cgi?id=1012623
https://bugzilla.redhat.com/show_bug.cgi?id=1155245