[FFe] juju 2.0

The juju team is requesting an FFE for juju. Juju-2 represents API changes and new features and bugfixes for juju. This FFE is intended to cover the acceptance of the updated juju package.

Timeline
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We have released 18 betas and 2 rc's of juju-2 so far over the xenial and now yakkety release cycles. We anticipate the final version to release on the same day as yakkety. We plan to do a soon after release SRU to bring the final version in. These RC versions are upgradable to 2.0 final, and can be considered usable for production deployments.

Upgrades
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Users coming from xenial have the same style packaging in place for juju-1 and juju-2. Juju 2 owns /usr/bin/juju, but juju-1 may divert this via the juju-1-default package.

Risks
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Juju 2.0 plans to release it's final version the same day as yakkety. We will need to SRU this into yakkety.

Quality / Testing
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We've continued our testing and bugfixing all throughout yakkety cycle. Juju itself practices continuous integration and testing of the juju source tree. All voting tests must pass for ubuntu before our final release. See http://reports.vapour.ws/releases/4438 for the CI test run that corresponds to rc2.