Handle more Nova and Neutron events

This introduces a simpler matching system for event types that supports
wildcard. We use this to grab all Nova instances notifications and a bit
more Neutron events.

We also change the get_event_types to a property to simplify the code a
bit.

Change-Id: Ica133ff2e9348a5d2640f068251d034bbd8a4f43
Merge "Handle more Nova and Neutron events"