Root+Disk on size, ReAdded openstack panel to providers

Updated the UI to show more details for size on instance screen and
new_instance screen. Serializer changes to add more data to size and identity
	modified:   api/serializers.py
	modified:   api/size.py
	modified:   core/models/size.py
	modified:   resources/js/cf2/views/instance_screen/instance_tabs_holder.js
	modified:   resources/js/cf2/views/new_instance_screen/instance_size_dropdown.js
migration necessary to add 'root'/'ephemeral' support to atmosphere providersize