EC2 VPC message validation - EUCA-9820

EC2 VPC request messages are now validated and a InvalidParameterValue
response is returned for invalid messages.

EUCA-9820
EC2 VPC changes now cause network view broadcast - EUCA-9823

The VPC service generates invalidation events for meaningful resource
changes. A VPC invalidation event listener requests a network broadcast
when an invalidation event occurs.

EUCA-9823