Add option to install openQA with bootstrap script

[baierjan]

Reference: https://progress.opensuse.org/issues/130369

Verification: https://openqa.opensuse.org/tests/3336996

Note: This test will not yet be scheduled.

[perlpunk]

#119 should fix the container test

[okurz]

I suggest to un-nest this by one level:

elsif (get_var('OPENQA_FROM_BOOTSTRAP')) {
    assert_script_run('zypper --no-cd -n in openQA-bootstrap');
    assert_script_run('skip_suse_specifics=1 skip_suse_tests=1 /usr/share/openqa/script/openqa-bootstrap', timeout => 1200);
}
else {
    install_from_repos;
} 

For a consistent style I would define a function though. install_containers is also just two lines. So make this

sub install_from_bootstrap {
    assert_script_run('zypper --no-cd -n in openQA-bootstrap');
    assert_script_run('skip_suse_specifics=1 skip_suse_tests=1 /usr/share/openqa/script/openqa-bootstrap', timeout => 1200);
}
…
elsif (get_var('OPENQA_FROM_BOOTSTRAP')) {
    install_from_bootstrap;
}
else {
    install_from_repos;
}