Comment 4 for bug 1732703

Commissioning logs: https://pastebin.canonical.com/203632/

The previous patch gave an error when only upstart was running, this should cover that case too (thanks ivanhitos):

def get_init_system():
    """Returns 'upstart' or 'systemd'."""
    if os.path.islink("/sbin/init"):
        initpath = os.readlink("/sbin/init")
        if initpath == "/lib/systemd/systemd":
            return 'systemd'
        else:
            return 'upstart'
    else:
        return 'upstart'