Always start transactions in quota cleanup methods
Always start transactions in quota cleanup methods

If the previous action that let to the quota reservation
cancelling was the result of a database connection getting
interrupted, attempting to query without calling session.begin()
will result in a sqlalchemy.exc.ResourceClosedError.

This alters the quota methods that mutate DB state to use a
transaction with the new oslo DB enginefacade decorators that
start a transaction for us.

Partial-Bug: #1596075
Partially-Implements: blueprint enginefacade-switch
Change-Id: I3d0539b11795cbcf97e70e1ec39013221a00d6d5

mahak/neutron,cloudbase/neutron,cloudbase/neutron,huntxu/neutron,eayunstack/neutron,sebrandon1/neutron,openstack/neutron,openstack/neutron,openstack/neutron,igor-toga/local-snat,sebrandon1/neutron,noironetworks/neutron,igor-toga/local-snat,eayunstack/neutron,mahak/neutron,mahak/neutron,noironetworks/neutron,huntxu/neutron