Create volume ignores allocated quota values of the parent project

We have discovered in Cinder that the sum of the allocated quotas and in_usage quotas can be greater than the the hard_limit quota of a project. The reason is that, by creating resources, first, Cinder tries to reserve the quota. Then, the method db.quota_reserve is called and there is no checking regarding the allocated values of the project (see https://github.com/openstack/cinder/blob/master/cinder/db/sqlalchemy/api.py#L872-L874).

Steps to reproduce:
1. openstack project create A

#grant the role admin to the user in this project.
2. openstack role add admin --project A --user admin

#create a subproject of A
3. openstack project create B --property parent_id=<project id of A>

#grant the role admin to the user in this project.
4. openstack role add admin --project B --user admin

#allocate all volume quota of project A to project B
5. openstack quota set <project id of B> --volumes 10

#create a volume in project A, it should not be allowed since it was allocated all the quota of project A to project B.
6. openstack volume create --size 1 test_volume

In the step 6, the volume isn't expected to be created because project A doesn't have any more free quota. But, in the current implementation, Cinder is allowing the creation of the volume.