Add netplan support

[cwxda]

Ubuntu 17.10 no longer uses /etc/network/interfaces, but netplan instead.
The context scripts won't configure network anymore atm

[vholer]

For this moment, you can fallback to the legacy ifupdown package and use Ubuntu 17.10 same way as previous systems configured via /etc/network/interfaces. This approach still works.

[trenton42]

This workaround no longer works in the upcoming 20.04 LTS release

[vholer]

Hello @trenton42 , is the ifupdown package going to be removed in 20.04 or the legacy scripts just stopped working. In both cases, a reference to the announcement (mailing list) or bugreport (in Ubuntu) would help us understand the problem to make the decision. Thank you! Vlastimil

[trenton42]

I think I spoke to soon, there was something else going on that prevented the legacy script from working. The ifupdown package is still available in 20.04, and the legacy script still works.

[openmilanese]

Test my personal netplan support. I forked today master branch and rewrite the patch. I have tested and it work ipv4 principal nic. Still pending for pull request review!