Add script to automate the change of docker registry

[João Victor Portal]

Brief Description
-----------------

The purpose of this issue is to add a script to the 'utilities' repository, to easily automate the change of registry URLs, type and credentials of a deployed StarlingX.

[Ghada Khalil (gkhalil)]

stx.6.0 - small operational enhancement

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/utilities/+/815084
Committed: https://opendev.org/starlingx/utilities/commit/1e7bbc6b33963681d2c175038b6dbb0b4dd4544e
Submitter: "Zuul (22348)"
Branch: master

commit 1e7bbc6b33963681d2c175038b6dbb0b4dd4544e
Author: Joao Victor Portal <email address hidden>
Date: Thu Oct 21 20:40:40 2021 -0300

    Created script to change private registry config

    This script changes the needed system parameters in order to use a
    different registry in an already deployed StarlingX. To do this, it
    manipulates the system parameters 'url', 'type' and 'auth-secret' of
    service 'docker'. Each one of these three parameters may exist inside
    the docker service sections 'docker-registry', 'elastic-registry',
    'gcr-registry', 'ghcr-registry', 'k8s-registry' and 'quay-registry'.

    The tests below were executed using a StarlingX dev build.
    The regression tests were not executed, as this script is not executed
    unless the user calls it.

    Test Plan:

    PASS: In a AIO-SX deploy with no parameters present, execute the script
    with 4 arguments (non-empty user and password), verify that the new
    registry is used to download images.
    PASS: In a AIO-SX deploy with all parameters present, execute the script
    with 4 arguments (non-empty user and password), verify that the new
    registry is used to download images.
    PASS: In a AIO-SX deploy with no parameters present, execute the script
    with 2 parameters (no user or password given), verify that the new
    registry is used to download images.
    PASS: In a AIO-SX deploy with all parameters present, execute the script
    with 2 parameters (no user or password given), verify that the new
    registry is used to download images.
    PASS: In a distributed cloud scenario, reconfigure the central cloud
    with a different private registry, verify that the new registry is used
    to download images, then check that new images downloaded by central
    cloud are being successfully downloaded in the subclouds.

    Closes-Bug: 1948491
    Signed-off-by: Joao Victor Portal <email address hidden>
    Change-Id: I3e10486333964264c8754c519163083a821eb54e

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/utilities/+/815760

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/utilities/+/815760
Committed: https://opendev.org/starlingx/utilities/commit/e85e2e544f470478c25f3ac9492dfdaf637607be
Submitter: "Zuul (22348)"
Branch: master

commit e85e2e544f470478c25f3ac9492dfdaf637607be
Author: Joao Victor Portal <email address hidden>
Date: Wed Oct 27 18:56:02 2021 -0300

    Added new script to '/usr/local/bin' folder

    Added the new utility script 'change_system_private_registry.sh' to the
    '/usr/local/bin' folder.

    Test Plan:

    PASS: Create an AIO-SX using a new ISO created with this change and
    verify that the file '/usr/local/bin/change_system_private_registry.sh'
    is present and is executable.

    Closes-Bug: 1948491
    Signed-off-by: Joao Victor Portal <email address hidden>
    Change-Id: Ied984fdcca6b702cef22451fedbb2edda190401b