Plugins » Katello

Fixes #16053: hooks for puppet 4 upgrade

This enables a `--upgrade-puppet` flag that will upgrade a Katello
installation from Puppet 3 to Puppet 4.

Most of this is based on
http://projects.theforeman.org/projects/foreman/wiki/Upgrading_from_Puppet_3_to_4
and https://github.com/beav/forklift/pull/1.

This is a squash commit that does not have full authorship info,
Stephen Benjamin authored significant portions of this patch.

Refs #16053: docs for puppet 3 to puppet 4 upgrade

TODO:

- [X] general overview of what happens (basically the expected "before" and "after" states)
- [X] rough ETA of how long the process takes, and if it scales out with number of hosts or anything like that (I am pretty sure it's constant-ish time but need to confirm)
- [X] links to info about rewriting modules to support puppet 4
- [X] document [flag day](https://en.wikipedia.org/wiki/Flag_day_(computing)) style upgrade, where Katello and all capsules are upgraded in a single outage window.
- [X] document gradual cutover upgrade, where users spin up a new puppet 4 capsule, move systems over, then decommission puppet 3 capsule at a later date.
- [X] docment special considerations for self-registered Katello installations
- [X] confirm and document that puppet 3 and 4 can't coexist on the same katello server
- [X] links to more info

Merge pull request #386 from beav/p4-upgrade

Fixes #16053: hooks for puppet 4 upgrade

Merge pull request #294 from beav/p4

Refs #16053: docs for puppet 3 to puppet 4 upgrade