Always run download_packages() after executing buildpackage SLS

By restricting this function call to when the script is successful, we
end up losing the log file from buildpackage.py when it fails, making it next to
impossible to troubleshoot. This commit makes jenkins retrieve at least
the log file, no matter what happens.
Merge pull request #18663 from terminalmage/buildpackage-jenkins-adjustment

Always run download_packages() after executing buildpackage SLS