Nested Quota: Set default values to subproject

Nested Quota: Set default values to subproject

In case of hierarchical projects set the default value
(for resources who have the resource flag set) for a
sub-project to zero. This patch adds this functionality for
hierarchical projects, while keeping the functionality
intact for non-hierarchical project. At the top level,
project resources will get the default values as imposed
by the "default" class settings.

Co-Authored-By: Erickson Santos <erickson@lsd.ufcg.edu.br>
Change-Id: I3b357464d5e5e0aa065506ac1e9d908e87f45c63
Partially-Implements: bp cinder-nested-quota-driver