Patchback of new runtime puppet manifests can cause failures

[Don Penney]

Brief Description
-----------------
Patchback of new runtime classes can be problematic due to the rollout of patches through a system. Sysinv on the controller could be patched ahead of a remote host and try to apply a newly introduced runtime class, which would cause a failure on the remote host because the class does not exist.

In order to facilitate patchback of new runtime classes, we'll introduce a set of extension classes that can be safely applied. The patch can update an unused extension class to reference the new runtime class, and sysinv can then safely apply the extension class (rather than the new class directly).

Severity
--------
Minor

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/stx-puppet/+/795384

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/stx-puppet/+/795384
Committed: https://opendev.org/starlingx/stx-puppet/commit/8390d6973e205a4af4d9ea9c8887183cb9dbb63a
Submitter: "Zuul (22348)"
Branch: master

commit 8390d6973e205a4af4d9ea9c8887183cb9dbb63a
Author: Don Penney <email address hidden>
Date: Mon Jun 7 12:27:57 2021 -0400

    Introduce runtime extension classes for patchability

    This update introduces a set of empty extension classes that can be
    used in patches to safely introduce new runtime classes. The patch can
    update an unused extension class to include the new runtime class,
    allowing sysinv to be patched to apply the selected extension class
    rather than the new runtime class directly. This allows sysinv to
    safely apply the class on a remote host, even if the host has not yet
    been patched.

    Closes-Bug: 1931270
    Signed-off-by: Don Penney <email address hidden>
    Change-Id: I302d7100a52d085aa5c58f80173edb5cfd490054