This changes instances, cores, and ram from ReservableResources to
CountableResources and replaces quota reserve/commit/rollback with
check_deltas accordingly.
All of the reservation and usage related unit tests are removed because:
1. They rely on some global QuotaEngine resources being
ReservableResources and every ReservableResource has been removed.
2. Reservations and usages are no longer in use anywhere in the
codebase.
Part of blueprint cells-count-resources-to-check-quota-in-api
Change-Id: I9269ffa2b80e48db96c622d0dc0817738854f602