Distributed cloud: overlapping admin network subnets are possible

[Steven Webster]

Brief Description
-----------------

    In a scenario with multiple subclouds configured initially with the
    management network, it is possible to update them to use admin
    networks having overlapping subnets. This can cause issues such as
    routing.

    If a subcloud is initially provisioned using the admin network,
    this condition is prevented.

Severity
--------
Minor: System/Feature is usable with minor issue

Steps to Reproduce
------------------

    - Provision a distributed cloud system with two subclouds using the management network
    - Create an admin network on the first subcloud.
    - Create an admin network on the second subcloud using the same
      subnet as the first.
    - Update the first subcloud to use the admin network.
    - Update the second subcloud to use the admin network.

Expected Behavior
------------------
The second subcloud should not have been able to reuse the first subcloud's subnet

Actual Behavior
----------------
The second subcloud is updated and uses the same subnet as the first

Reproducibility
---------------
100%

System Configuration
--------------------
Distribued cloud system with at least two subclouds.

Branch/Pull Time/Commit
-----------------------
master

Last Pass
---------
N/A

Timestamp/Logs
--------------
N/A

Test Activity
-------------
Evaluation

Workaround
----------
Do not use the same admin subnet on two subclouds.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/distcloud/+/923456

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/distcloud/+/923456
Committed: https://opendev.org/starlingx/distcloud/commit/6e2af84deb30af871ef14e937de2a3619d482842
Submitter: "Zuul (22348)"
Branch: master

commit 6e2af84deb30af871ef14e937de2a3619d482842
Author: Steven Webster <email address hidden>
Date: Wed Jul 3 19:22:13 2024 -0400

    Add admin network validation on network reconfig

    In a scenario with multiple subclouds configured initially with the
    management network, it is possible to update them to use admin
    networks having overlapping subnets. This can cause issues such as
    routing.

    If a subcloud is initially provisioned using the admin network,
    this condition is prevented. This commit extends that validation
    to network reconfiguration.

    Test Plan:

    - Provision a system with two subclouds using the management network
    - Create an admin network on the first subcloud.
    - Create an admin network on the second subcloud using the same
      subnet as the first.
    - Update the first subcloud to use the admin network.
    - Update the second subcloud to use the admin network. Ensure an
      error message is returned to the user indicating overlapping
      subnets.
    - Ensure the subclouds can be updated to use the management network
      again

    Closes-Bug: 2071835

    Change-Id: Iab783733912c7566a90d6fa872348a0d14a172e5
    Signed-off-by: Steven Webster <email address hidden>