Optimize "QosPolicy" OVO bound objects retrieve methods

[Rodolfo Alonso]

The following methods are inefficient:
- get_bound_networks
- get_bound_ports
- get_bound_floatingips
- get_bound_routers

Those methods, using the "QosPolicy_XXXX_Binding" OVO interface, are retrieving all objects with a certain policy ID and then returning only the ID of the _XXXX_ object. That means we retrieve a full register list from the DB, then those registers are converted to OVO and then we extract only the _XXXX_ ID.

This is obviously inefficient, regardless of the simplicity of the "QosPolicy_XXXX_Binding" OVO and the 1:1 parity to the DB associated register. We should instead only retrieve the _XXXX_ object ID from the DB and return it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/726358

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/726358
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=1f018514d71daab6ff3d4bd508318ce8ed8d1045
Submitter: Zuul
Branch: master

commit 1f018514d71daab6ff3d4bd508318ce8ed8d1045
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Fri May 8 11:32:17 2020 +0000

    Optimize QoS bound objects queries

    Optimize the following methods:
    - get_bound_networks
    - get_bound_ports
    - get_bound_floatingips
    - get_bound_routers

    Those methods, using the "QosPolicy_XXXX_Binding" OVO interface, were
    retrieving all objects with a certain policy ID and then returning
    only the ID of the _XXXX_ object. That means to retrieve a full
    register list from the DB, then converted them to OVOs and extract
    only the _XXXX_ ID.

    This patch retrieves only the _XXXX_ object IDs from the DB and
    returns the list, without the OVO conversion.

    Change-Id: I891eba93b3b4abaec8ada13a032b5440cbb0548d
    Closes-Bug: #1877560