[placement][ptg] Allocation Partitioning
> When a /usages query is made, the consumer type could be optionally
> expressed, limiting results. Are multiple types something that needs
> to be expressed in one query? Not yet discussed.
I expect that Nova's quota stuff will want to be able to express
multiples, FWIW. However, I think I can say for sure that the usage
result will be the most useful for quota behavior if it returns usages
grouped by type (whether or not a subset of types were in a filter