remove-machine fails to remove machines in rackspace/openstack

https://github.com/juju/juju/pull/7175

Easy reproducer in the PR.

This is still failing sometimes in 2.3.

I think the issue is that the host machine is taking a long time to provision, and the container sits there in the "dying" state during that time. When the host finally comes up, its machine agent sees the container is dying and proceeds to remove it from state.

We should short-circuit the removal of containers when the host machine hasn't yet been provisioned.

So that was not quite right. From the machine agent log of the host, I can see that container provisioner is failing because it can't install lxd-client from the archives:

"""
E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/l/lxd/lxd-client_2.0.11-0ubuntu1~16.04.2_amd64.deb 404 Not Found [IP: 201:67c:1360:8001::17 80]

E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
"""

Then in cloud-init-output.log:

"""
Err:1 http://security.ubuntu.com/ubuntu xenial-security InRelease
  Temporary failure resolving 'security.ubuntu.com'
Err:2 http://archive.ubuntu.com/ubuntu xenial InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Err:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Err:4 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
  Temporary failure resolving 'archive.ubuntu.com'
Reading package lists...
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/InRelease Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/InRelease Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/InRelease Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/InRelease Temporary failure resolving 'security.ubuntu.com'
W: Some index files failed to download. They have been ignored, or old ones used instead.
Reading package lists...
"""

I still think we should short-circuit the removal of containers, but the more important issue here is to stop apt flaking out.

https://github.com/juju/juju/pull/8268