Juju 1.20 release branch

[Ian Booth]

Hi folks

The Juju 1.19.4 release will serve as a release candidate for Juju 1.20, the
next stable release. There are still a couple of known bugs to fix before 1.20
goes out the door. To allow trunk development to continue unabated, a 1.20
branch has been forked off the rev used to cut 1.19.4:

https://github.com/juju/juju/tree/1.20

Any commits to the 1.20 branch will of course need to be ported forward to trunk.

CI has been set up to monitor changes to the 1.20 branch, and we'll also have a
landing job set up to gate commits to the branch (real soon now). As with
previous releases, we won't release until CI is happy.

The 1.20 milestone with bugs needing to be fixed before release is here:

https://launchpad.net/juju-core/+milestone/1.20.0


Thanks,
Ian