Add CONTEXT_READER to "get_reservations_for_resources"
Add CONTEXT_READER to "get_reservations_for_resources"

The method executes DB operations outside a DB context and with an
inactive session.

Change-Id: Ifd1c7b99421768dfa9462237e2b1b14af0e68f41
Closes-Bug: #1930876

mahak/neutron,mahak/neutron,mahak/neutron,openstack/neutron,openstack/neutron,openstack/neutron