Event-driven optimization based

The blueprint "continuously-optimization" [1] give the possibility to the administrator to periodically trigger an audit but not to react to a situations and changes in system.

We propose an event-driven optimization-based audit control. We wants to select among a list of events which may trigger the audit :
- React to a predicted situation.
- React to a critical situations and changes in system (e.g: threshold )
- A new compute node has been added to the cluster
- A compute node has been removed from the cluster
- A new virtual machine has been created

The events can be created by AODH, congress, ceilometer, scoring engine (long term)

Here is the use case summarizing the previous elements:

   Given that I am an audit
   And I have auto-triggering event handlers set up
   When I receive an alarm notification from AODH/Congress/...
   And that event matches my audit-triggering criteria
   Then I should execute myself.

Note : This blueprint could potentially be implemented by periodic optimizations, but preferably would be more async than periodic.

[1] https://blueprints.launchpad.net/watcher/+spec/continuously-optimization