Create action: num-instances

[Alvaro Uria]

In order to script a verification of safe removal of nova-compute units, a new action would be required.

* Action name: num-instances
Return the number of instances running, suspended and stopped.

[Martin Kalcok (martin-kalcok)]

PR is opened with slight change that renames the action to `instance-count`.

https://review.opendev.org/c/openstack/charm-nova-compute/+/783371

[Aurelien Lourot (aurelien-lourot)]

Added charm-guide as affected project in order to write release notes.

[Peter Matulis (petermatulis)]

This never got added to the 21.04 release notes.

[Alex Kavanagh (ajkavanagh)]

> This never got added to the 21.04 release notes.

Peter, the review is still active; the feature didn't make it into 21.04, AFAICT?

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-nova-compute/+/783371
Committed: https://opendev.org/openstack/charm-nova-compute/commit/5eea014dd5e56c3205e1defbdc6253c5fbd8953a
Submitter: "Zuul (22348)"
Branch: master

commit 5eea014dd5e56c3205e1defbdc6253c5fbd8953a
Author: Martin Kalcok <email address hidden>
Date: Fri Mar 26 17:08:54 2021 +0100

    Add action that returns number of running VMs on the unit.

    Closes-Bug: #1911011
    Change-Id: If9ae646bc91b6389876830843bbf905596963054
    func-test-pr: https://github.com/openstack-charmers/zaza-openstack-tests/pull/535

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/charm-guide/+/796873

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-guide/+/796873
Committed: https://opendev.org/openstack/charm-guide/commit/d06d415cddfe6fa36217af175eb50d98c17a8483
Submitter: "Zuul (22348)"
Branch: master

commit d06d415cddfe6fa36217af175eb50d98c17a8483
Author: Peter Matulis <email address hidden>
Date: Thu Jun 17 10:52:52 2021 -0400

    Add new nova-compute action to RNs

    Also fix up wording for the Glance section.

    Partial-Bug: #1911011
    Change-Id: I288b5eb8221aedb061b826288cfc102d74e96793