After dist upgrade Juju 1.X should still be the default

[Martin Packman]

When upgrading to Xenial the new default Juju version is going to be 2.0.

Because 2.0 clients are not compatible with 1.X environments, this means existing environments will be inaccessible unless the 1.X client is switched to. The plan is to give a warning when creating Juju 2 configuration for the first time, something along the lines of:

Feedback suggests that we should correct this by having juju 1.X be the higher priority in update alternatives.

Product management has give feedback that the preference it to push toward the direction of Juju 2 at all times. Since this process would default to Juju 1 if a Juju 2 users installs Juju 1 for legacy reasons, we are instead going to implement the following:

    $ sudo apt-get update

    $ juju status
    WARNING Creating new juju 2 configuration.
    Use `update-alternatives --config juju` to switch
    for 1.X environments.

    $ juju status
    ERROR Unable to connect to model "".
    Please check your credentials or use 'juju bootstrap' to
    create a new model.

[Richard Harding (rharding)]

See bug https://bugs.launchpad.net/juju-core/+bug/1564622 for the fix in Juju to properly output the messaging to the user.

[Nicholas Skaggs (nskaggs)]

We fixed bug 1564622, along with creating a juju-1-default package in xenial to alleviate this issue. Juju 2.0 is the default /usr/bin/juju and will remain as such in Xenial, regardless of the installation path.