Allow ironic_ipxe to serve instance images

Ironic provides a feature to allow instance images to be served from a
local HTTP server [1]. This is the same server used for PXE images with
iPXE. This does not work currently because the ironic_ipxe container
does not have access to /var/lib/ironic/images (ironic docker volume),
where the images are cached. Note that to make use of this feature, the
following is required in ironic.conf:

[agent]
image_download_source = http

This change fixes the issue by giving ironic_ipxe container access to
the ironic volume.

[1] https://docs.openstack.org/ironic/latest/admin/interfaces/deploy.html#deploy-with-custom-http-servers

Change-Id: I501d02cfd40fbacea32d551c3912640c5661d821
Closes-Bug: #1856194

ansible/roles/ironic/defaults/main.yml

@@ -146,6 +146,7 @@ ironic_pxe_default_volumes:
 ironic_ipxe_default_volumes:
   - "{{ node_config_directory }}/ironic-ipxe/:{{ container_config_directory }}/:ro"
   - "/etc/localtime:/etc/localtime:ro"
+  - "ironic:/var/lib/ironic:ro"
   - "ironic_ipxe:/httpboot/"
   - "kolla_logs:/var/log/kolla"
 ironic_inspector_default_volumes:

releasenotes/notes/ironic-ipxe-instance-image-47fb3c9f0edef5f5.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixes an issue with the ``ironic_ipxe`` container serving instance images.
+    See `bug 1856194 <https://bugs.launchpad.net/kolla-ansible/+bug/1856194>`__
+    for details.