Make aggregate filters use objects

Some scheduler filters that use aggregates have been converted
to use nova objects. This patch converts the remaining ones to
use objects. In both cases the calls to the database are
replaced by calls to a utility method that gets the required
data using Aggregate objects. In the future these utility
methods could be replaced with an implementation that works on
a cache - for now they do not change the behavior - its just
a refactor.

blueprint kilo-objects
Change-Id: I42d5697a67805b7e85f82cf3cf2cd6e17d923955
Merge "Make aggregate filters use objects"