"280.003 Subcloud Backup Failure" alarm is not removed after unmanaging/deleting subcloud

[Christopher de Oliveira Souza]

Brief Description
---------------------
When the subcloud backup fails, the 280.003 alarm is not removed after unmanaging/deleting the subcloud.

Severity
---------------------
Minor.

Steps to Reproduce
---------------------
    Create subcloud backup
    dcmanager subcloud-backup create --subcloud subcloud1 --sysadmin-password Li69nux*
    Watch Ansible logs and power off (or sudo reboot) the subcloud after reaching the following task: "Run subcloud1 backup playbook"
    Backup fails as it cannot connect to the subcloud (it will take some minutes)
    'Failed to connect to the host via ssh: ssh: connect to host 2620:10a:a001:a103::1016 port 22: No route to host'
    Check Backup status goes to 'failed' state
    Check 280.003 alarm using 'fm alarm-list'
    Unmanage/Delete the subcloud
    Wait some time and re-check 'fm alarm-list'. The alarm will be there even after deleting the subcloud.

Expected Behavior
----------------------
The alarm cleared after deleting the subcloud

Actual Behavior
----------------------
The alarm is still present after deleting the subcloud.

Reproducibility
----------------------
1 out of 1.

System Configuration
----------------------
Distributed Cloud

Load info (eg: 2022-03-10_20-00-07)
---------------------
22.12 - 2022-12-18_09-30-35

Last Pass
---------------------
NA

Timestamp/Logs
----------------------
// Alarm
280.003 | Subcloud Backup Failure (subcloud=subcloud1) | subcloud=subcloud1 | minor | 2022-12-28T14:17:12.924253

Alarms
---------------------
NA

Test Activity
---------------------
Feature testing

Workaround
---------------------
NA.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/distcloud/+/872643

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/distcloud/+/872643
Committed: https://opendev.org/starlingx/distcloud/commit/591a06e858526f23ccd85e5a684903d0b0e6d156
Submitter: "Zuul (22348)"
Branch: master

commit 591a06e858526f23ccd85e5a684903d0b0e6d156
Author: Christopher Souza <email address hidden>
Date: Fri Feb 3 07:57:07 2023 -0300

    Clear 280.003 alarm on subcloud deletion

    When a subcloud was deleted, the 280.003 alarm was not cleared.
    The change was to add the 280.003 alarm to the list of alarms that are checked.

    Test Plan:

    PASS: Install and bootstrap DC.
    PASS: create a subcloud backup and power off the subcloud after reaching:
    "Run subcloud1 backup playbook".
    PASS: Wait for the alarm 280.003 to be set, then umanage and
    delete the subcloud and check if the 280.003 alarm was cleared.

    Closes-bug: 2004638

    Signed-off-by: Christopher Souza <email address hidden>
    Change-Id: I70458b1fe6da4b9c0bf458ee57720a4ffaeafbfb