jenkins: build.conf: DOCKER_IMAGE_BASE has no effect

[Davlet Panech]

Brief Description
-----------------
The parameter DOCKER_IMAGE_BASE has no effect in Jenkins build scripts, https://opendev.org/starlingx/jenkins-pipelines/src/commit/4ca6302a88e61a276ecf48dbc98396e1ae5cd0d1/scripts/templates/build.conf.example.in#L176 .

Severity
--------
Minor

Steps to Reproduce
------------------
In build.conf: set DOCKER_IMAGE_BASE to starlingx/stx-debian:master-stable-latest
Run the build, or re-run the build-images step.
Examine the logs from the build-images step.

Expected Behavior
------------------
Log files indicate we are using starlingx/stx-debian:master-stable-latest as the base image.

Actual Behavior
----------------
Log files indicate we are using the timestamped image (ie the one generated by the current build).

Reproducibility
---------------
Reproducible

System Configuration
--------------------
N/A

Branch/Pull Time/Commit
-----------------------
master/2023-05-10

Last Pass
---------
N/A

Timestamp/Logs
--------------
N/A

Test Activity
-------------
N/A

Workaround
----------
N/A

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/jenkins-pipelines/+/882442
Committed: https://opendev.org/starlingx/jenkins-pipelines/commit/9a6f15d7d0b911ace6fe00c6c46b10a4e18b743a
Submitter: "Zuul (22348)"
Branch: master

commit 9a6f15d7d0b911ace6fe00c6c46b10a4e18b743a
Author: Davlet Panech <email address hidden>
Date: Fri May 5 09:32:08 2023 -0400

    docker-images: fix misspelled DOCKER_IMAGE_BASE

    * build-docker-images.sh
      - DOCKER_IMAGE_BASE was spelled as DOCKER_BASE_IMAGE - fixed
      - skip base image pull when using stx-debian

    Closes-Bug: 2019135
    Signed-off-by: Davlet Panech <email address hidden>
    Change-Id: Ib0aa252889312d78e21898c38edd86579c00f7ce