Removed update_instance_history to do things right

Took out all the bad logic in update_instance_history in place of model methods
on core.Instance

now just call core_i.update_history(status_name, task_name, first_update(opt) )
and all problems are solved with *magic* :)

NOTE: api/serializers.py fails if you want to debug it.
	modified:   api/instance.py
	modified:   api/serializers.py
	modified:   core/models/instance.py
	modified:   service/allocation.py
	modified:   service/tasks/allocation.py