Reproducer bash script sets USER_PYTHON_OVERRIDE=python2

[Ronelle Landy]

When running the reproducer on rhel 8 and other platforms that support python3, we should not force a python2 install.

https://github.com/openstack/tripleo-quickstart-extras/blob/master/roles/create-zuul-based-reproducer/templates/reproducer-zuul-based-quickstart.sh.j2#L188

We can't only support python2.

[Ronelle Landy (rlandy)]

install-deps will force python_cmd to be python_2 unless it's set.
We need to set USER_PYTHON_OVERRIDE for rhel-8 to be python-3.

In fact, this can never work ...

python_cmd() {
    distribution=unknown
    distribution_major_version=unknown
    # we prefer python2 because on few systems python->python3
    python_cmd=${USER_PYTHON_OVERRIDE:=python2}

    if [ -f /etc/os-release ]; then
        . /etc/os-release
        distribution_major_version=${VERSION_ID%.*}
        case $NAME in
        "Red Hat"*) distribution="RedHat"
            if [ "$distribution_major_version" -ge "8" ]; then
                python_cmd=${USER_PYTHON_OVERRIDE:=python3}
            fi

If we don't export the override, python_cmd will be set to python2 and not be reset

[Ronelle Landy (rlandy)]

This is fixed through other patches