Public IP released when pending instance terminated - EUCA-4735

We now handle clean up of the system assigned public IP address for an
instance when it is terminated immediately after launch.

EUCA-4735
Removed public IP clean up rollback for terminated instance - EUCA-4735

When an instance enters the terminated state we now make a final attempt
to clean up the public address. If dispatching the unassign message to
the cluster controller fails we will not rollback the unassignment.

EUCA-4735
Merge remote-tracking branch 'origin/dev/sjones/EUCA-4735' into testing