Custom host field in Nova Compute Ironic

[Doug Szumski]

Customising the host field under the [DEFAULT} section in nova.conf for Nova Compute Ironic breaks the "Waiting for nova-compute services to register themselves" task in the nova-cell role when Ironic is enabled.

For example, provide the following config file:

```
[DEFAULT]
host = ironic
```

Put it here:

/etc/kolla/config/nova/nova-compute-ironic.conf

Make sure Ironic is enabled.

Run:

kayobe overcloud service reconfigure -kt nova

This task never succeeds, even though the Nova Compute Ironic service starts fine.

```
TASK [nova-cell : Waiting for nova-compute services to register themselves] ***********************************************************************************************
FAILED - RETRYING: [doug-aio]: Waiting for nova-compute services to register themselves (20 retries left).
FAILED - RETRYING: [doug-aio]: Waiting for nova-compute services to register themselves (19 retries left).
```

See this spec for why you would want to customise the host name:

https://specs.openstack.org/openstack/nova-specs/specs/2024.1/approved/ironic-shards.html#migrate-from-peer-list-to-single-nova-compute

Note that even for small deployments, not using shards, it is still useful to have a custom host name (to make easier to fail over the Nova Compute Ironic service).

The bug exists because the "Waiting for" task assumes the host field will always be set to <hostname>-ironic.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/912483