Systemd image can't set hostname from DHCP when polkit is not installed

[jonesmz]

For the lite image, we don't typically install polkit, which prevents systemd-hostnamed to be used to configure the system hostname via either hostnamectl or systemd-networkd.

This isn't a problem for the desktop image, which does install polkit.

Personally I'm not sure bringing polkit into the lite image is worth the extra cruft, so for now this issue won't be actioned.