Comment 6 for bug 1714028

The artful image is ifupdown free (for some time) the failing cases we've found we're related to a few things:

1) curtin currently installs ifenslave if it gets a network config with bonds in it; this in turn installs ifupdown (it's a proper dependency since it provides ifupdown hooks); however on artful there is no need. Curtin will now filter out ifenslave dep if the target image is artful.

2) serveral curtin tests set IPV6 MTU values, this fails to render in netplan since netplan/networkd dont currently support configuring IPV6 mtu (https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1671951)

3) bridging was failing in artful due to netplan enables STP by default; this prevents setting forwarding delays < 2 seconds (we currently test disabling forwarding delay) so we set STP off and fd of 0; however cloud-init doesn't support rendering netplan stp configuration (https://bugs.launchpad.net/cloud-init/+bug/1721157) so cloud-init will need a fix to render the correct value for bridge stp settings.