tripleo-build-containers-ubi-8 fails - 'release' is undefined

[Marios Andreou]

At [1][2] the tripleo-build-containers-ubi-8 job is failing during the setup for container image build with trace like:

 2021-10-18 08:21:58.911048 | TASK [build-containers : Generate tripleo building script]
 2021-10-18 08:22:09.830596 | primary | ERROR
 2021-10-18 08:22:09.831237 | primary | {
 2021-10-18 08:22:09.831360 | primary | "msg": "AnsibleUndefinedVariable: 'release' is undefined"
 2021-10-18 08:22:09.831467 | primary | }

Looks like the issue was introduced by [3]. We can try to use 'release' if it is defined otherwise we can fall back to using 'branch' as before. If that doesn't work then we can just pass 'release' in the build-containers-ubi-8 job.

[1] https://e77644a1825734c4b1a5-64bde2a99f8c0525b91ac2e42ffc128a.ssl.cf1.rackcdn.com/813975/2/check/tripleo-build-containers-ubi-8/ee0354f/job-output.txt
[2] https://5a035c34399aaf265f61-e6ddc7380eb470b6a5615640c6b2397b.ssl.cf1.rackcdn.com/813975/2/check/tripleo-build-containers-ubi-8/22843bf/job-output.txt
[3] https://opendev.org/openstack/tripleo-ci/commit/34abe11d4c18e0bd846d6a3be4d45d00b8277f86

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/tripleo-ci/+/814400

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/tripleo-ci/+/814400
Committed: https://opendev.org/openstack/tripleo-ci/commit/ed8fdff6ff618b78e7fcf5f6d2419514fba4f903
Submitter: "Zuul (22348)"
Branch: master

commit ed8fdff6ff618b78e7fcf5f6d2419514fba4f903
Author: Marios Andreou <email address hidden>
Date: Mon Oct 18 13:17:29 2021 +0300

    Try to use 'release' for container image build - fallback to branch

    In [1] the container build template was updated to use 'release'
    rather than 'branch' var. However this is not defined for the
    build-containers-ubi-8 job resulting in related-bug. Instead we
    can try to use 'release' and fall back to 'branch' if release
    is not defined.

    Change-Id: Ifee7bf97ef30056ffac0ac381e4ea36f5c491a2c
    Related-Bug: 1947572