Add --initial-password option to update-iso.sh

[Victor Romano]

Brief Description
-----------------
Sometimes it's necessary to have a way to change the initial sysadmin password of a node during the initial install. It was found difficult to do via the ks-addon.cfg file. The update-iso,sh file should provide a new option, --initial-password <password> which can properly handle this functionality.

Severity
--------
Minor

Steps to Reproduce
------------------
Attempts to change the initial password required writing to the shadow file for it to be successful.

Expected Behavior
------------------
A clear procedure to update the initial password inside the ISO.

Actual Behavior
----------------
No direct and simple way to update ISO password.

Reproducibility
---------------
100% reproducible

System Configuration
--------------------
NA

Branch/Pull Time/Commit
-----------------------
NA

Last Pass
---------
This was less of an issue in centos.

Timestamp/Logs
--------------
NA

Test Activity
-------------
NA

Workaround
----------
NA

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/utilities/+/879059

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/utilities/+/879059
Committed: https://opendev.org/starlingx/utilities/commit/23e19ff7646bb8823fb388819c2e38a58520295d
Submitter: "Zuul (22348)"
Branch: master

commit 23e19ff7646bb8823fb388819c2e38a58520295d
Author: Victor Romano <email address hidden>
Date: Thu Mar 30 13:13:49 2023 -0300

    Add initial password option to update-iso.sh

    Sometimes, for security purposes, the user might want to change on the
    ISO the initial password prompted on first login, that is "sysadmin"
    by default. This change adds the --initial-password option to
    address this. The user will still be prompted to change the password
    on first login regardless.

    Test plan:
      PASS: Run update-iso.sh with --initial-password, install the new ISO
            and verify that the provided password is the initial password.
      PASS: Run the same test with different ISO builds.

    Closes-Bug: 2013365

    Signed-off-by: Victor Romano <email address hidden>
    Change-Id: I267968f322771a0a3d17c0ad7742ebd401d9b08e