Implemented an alternative stop_all_instances and destroy_all_instances.
Stop, start, resume and suspend need to add and remove floatingips before it's
useful to stop or suspend all instances.
Implemented stop_instance task but there is no related start_instance task yet
so I commented it out.
Moved all tasks to the get_driver method instead of having copied code all over.
	modified:   service/meta.py
	modified:   service/tasks/driver.py
Fixed problem with circular dependency in service.tasks.driver. With OSDriver.