following changes
- introduced notion of event bus with publish, subscribe, unsubscribe
semantics
- a plug-in can implement the EventBus abstraction to provide event
bug to CloudStack
- A rabbitMQ based plug-in that can interact with AMQP servers to
provide message broker based event-bug
- stream lines, action events, usage events, alerts publishing in to
convineance classed which are also used to publish corresponding
event on to event bus
- introduced notion of state change event. On a state change, in the
state machine corrsponding to the resource, a state change event is
published on the event bug
- associated a state machined with Snapshot and Network objects
- Virtual Machine, Volume, Snaphost, Network object state changes wil
result in a state change event
