debian: Use minbase variant type for debootstrap.

[Chuck Short]

We should be using the minbase variant when running debootstrap while creating the image. This will:
- increase the speed of the build-image
- decrease the footprint size of the base image
- Allow to include starlingx changes on top of the base image.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/tools/+/827164

[Chuck Short (zulcss)]

This is a temporary workaround in order to have LAT use the variant option.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/tools/+/827164
Committed: https://opendev.org/starlingx/tools/commit/a2a8ce7834e0454f139a05423331c0a73501f0dc
Submitter: "Zuul (22348)"
Branch: master

commit a2a8ce7834e0454f139a05423331c0a73501f0dc
Author: Charles Short <email address hidden>
Date: Mon Jan 31 18:04:17 2022 +0000

    debian: Use minbase variant for debootstrap

    By default debootstrap creates a base Debian installation with all
    packages of a priority required and important. This includes packages
    such as systemd, systemd-sys, and systemd-timesyncd. This creates a
    race condition when debootstrap is complete and then the starlingx
    packages are updated after. This is most notable while trying to
    install ntpd and systemd-timesyncd is already installed.

    When using the minbase variant debootstrap will only install the
    required packages in order to use a Debian system. This includes
    apt, base-files, base-passwd, bash, and etc. The full list of
    packages that are installed, can be determined by
    running the following command:

    dpkg-query -W --showformat='${Package}\t${Priority}\n' | grep "required$"

    Using the minbase variant option with debootstrap allows the build-image
    script to install the StarlingX packages over on top of the base
    system created by debootstrap.

    The side affect of this is that it will speed up image builds when
    using the build-image since debootstrap is only installing the
    required packages. Another benefit is that it will create
    a smaller /sysroot footprint.

    This dockerfile change is a temporary workaround so that
    LAT can add this change to the StarlingX Debian build system.
    Once this change has been added then it can be dropped.

    Test Plan
    PASS build docker containers with stx-init-env --rebuild
    PASS Build new ISO
    PASS Run new ISO and make sure that you get a login prompt.

    Partial-Bug: 1959607

    Signed-off-by: Charles Short <email address hidden>
    Change-Id: I858ff95d54808cefd816874e3029e92a240619f1

[Ghada Khalil (gkhalil)]

Marking as Fix Released based on the above commit. This should be sufficient for stx.7.0. If further work is required, a follow-up LP can be opened OR this can be tracked as a task under stx.8.0 Debian stories.