Code review comment for lp:~vishvananda/nova/quotas

I went ahead and made the first couple of changes. The idea of passing in requested volumes and returning allowed is to allow for the future possibility for requesting more than one volume (or address at a time). The current api allows for launching n instances, so it makes sense there to pass in num_requested and get a num_allowed back.

I agree that it is a bit awkward given the current api, but i think keeping the same logic that we use for instances makes sense for the future idea of creating multiple volume and multiple ips in a single call.