AZ support for cells

Conflicts:
	nova/api/metadata/base.py
	nova/api/openstack/compute/contrib/extended_server_attributes.py
	nova/availability_zones.py
	nova/cells/manager.py
	nova/cells/messaging.py
	nova/cells/rpcapi.py
	nova/cells/state.py
	nova/tests/compute/test_compute.py
fixup! Support sending to havana scheduler for run_instance