even when the bridge has no addresses, still use DHCP

[jameinel]

Description of change

We had a bug where we saw 'lxdbr0' exist, but it didn't have an IP address associated with it. (This is true at least on Xenial.) And our code was deciding that we should use DHCP under certain circumstances, but not under this one, and the default path was to use Static allocation.

QA steps

  $ juju bootstrap lxd
  $ lxc profile edit juju-default # add 'security.privileged: true'
  $ juju deploy cs:~jameinel/ubuntu-lite-nested

With stock 2.1, the nested container that comes up will have an /etc/network/interfaces file with a line like:

  iface eth0 inet manual

instead of

  iface eth0 inet dhcp

With this change, the nested container will be configured to use DHCP.

Documentation changes

Should just enable what used to work in 2.0.

Bug reference

lp:1664409

[axw]

LGTM. Can you leave a TODO to add a test for this?

[jameinel]

Sure, this was originally part of: my fix for https://bugs.launchpad.net/juju/+bug/1656326 which got reverted (issue #6933). But I realized I probably needed it here as well.

[jameinel]

Also note: lxc/lxd#2885
security.nesting = true doesn't seem to be enough because of their new changes around UID maps.

[jameinel]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/10292

[jameinel]

$$merge$$ the failure was in PubSub TestFirstMessage which I highly doubt is related.

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/10293

[jameinel]

$$merge$$ (also a bot failure vs an actual failure)

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/10297

[jameinel]

$$merge$$ lxd is failing to find instances

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju