Change-Id: Id5ed0b594d6270c4a03606caa776bbb291be2694

This allows us to add configuration scenarios.

Change-Id: Id636f78c61237fb27fa65fa3d4b3fc1a4cf0ba6a
Story: 2004360
Task: 40777

Switches to use the IPA builder project for building IPA images.

Switches the IPA images used by default to CentOS 8 based image.

Changes the file extension of the IPA kernel image from vmlinuz to
kernel.

Story: 2007070
Task: 37953

Change-Id: I82fc455f41f48dacb453e135870dd776895d7c99
Story: 2006574
Task: 39485

Change-Id: I10432c914e05cde6b07ff1250b2a5c9b0c796500
Story: 2007752
Task: 39942

The ironic-python-agent coreos images are unsupported and are
anticipated to be removed from the tarballs.openstack.org site.

In advance of this, we need to remove references to these images.

Change-Id: Ifb402418d7962cf507b190e028a59b94ad5d46ac

Diskimage builder supports specifying a list of packages to install via
-p. We currently support this for the root image, but not IPA images.

This change adds a new configuration option, 'ipa_build_dib_packages',
that should be a list of additional packages to install in locally built
IPA images. This affects the following commands:

kayobe seed deployment image build
kayobe overcloud deployment image build

This depends on
https://github.com/stackhpc/ansible-role-os-images/pull/25.

Also adds an example to the documentation for the equivalent option for
root image.

Change-Id: I04191d9541894b6a264e966c9ecb1056e0edade4
Story: 2006855
Task: 37446

Depends-On: https://review.opendev.org/690559/

Change-Id: I4e766424607317e5817d26461f7a1e180e9b2146
Story: 2004337
Task: 37378
Task: 37381