Upgrade stuck due to out-of-date distro-info-data package

[Paul Gear]

Scenario:

- Trying to upgrade controller from 2.0-rc3 to 2.0.0

Actions taken:

- juju switch controller
- juju upgrade-juju --dry-run
- juju upgrade-juju

Expected result:

- Successful upgrade

Actual result:

machine-0: 05:39:22 ERROR juju.worker.dependency "upgrader" manifold worker returned unexpected error: unexpectedly bad version "2.0.0.1-zesty-amd64" in tools storage: unknown OS for series: "zesty"

Workaround:

Upgrading disto-info-data package on the controller so that it included information about zesty and restarting jujud-machine-0 on the controller fixed the issue and the controller upgraded correctly.

[Anastasia (anastasia-macmood)]

Parts of the fix against
    * version: https://github.com/juju/version/pull/4
    * utils: https://github.com/juju/utils/pull/247

[Ian Booth (wallyworld)]

The upgrade will no longer break when parsing tools versions. There are other places in the code which do require an up to date distroinfo data eg the instance provisioner. The code has been modified to support up to zesty out of the box.

[Martin Packman (gz)]

Backporting this fix to 2.0 branch in:

<https://github.com/juju/juju/pull/6602>