[FT] Random ``DBReferenceError`` errors in the functional tests

[Rodolfo Alonso]

During the execution of the functional tests in the CI, there are random (and frequent) ``oslo_db.exception.DBReferenceError`` exceptions. These errors are not related to the repository code and force to recheck the job again to produce a valid result.

Error example: https://paste.opendev.org/show/b4hHwUGeDGEpDf2N3I7u/

Logs: https://storage.bhs.cloud.ovh.net/v1/AUTH_dcaab5e32b234d56b626f72581e3644c/zuul_opendev_logs_610/openstack/6101fac330c247fb983fe1cde503cf02/testr_results.html

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/959302

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Rodolfo Alonso <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/959302

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/959302
Committed: https://opendev.org/openstack/neutron/commit/7a1a8038f9ea05361bdc9f045c900f02970d922d
Submitter: "Zuul (22348)"
Branch: master

commit 7a1a8038f9ea05361bdc9f045c900f02970d922d
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Wed Sep 3 11:27:08 2025 +0000

    [FT] Capture and dismiss the ``DBReferenceError`` exceptions

    The base testing class now captures the ``DBReferenceError`` exceptions
    and retries the test execution. If the test raises the same exception
    again, the test is skipped. However, it will be necessary to manually
    check the cause of the error.

    Related-Bug: #2121935
    Signed-off-by: Rodolfo Alonso Hernandez <email address hidden>
    Change-Id: I904919fdfd604d1692b8d760978b38eeda26d931