private void amend(DeployState deployState, AdminModel adminModel) {
            for (HostResource host : adminModel.getAdmin().hostSystem().getHosts()) {
                if ( ! host.getHost().getChildrenByTypeRecursive(AmendedService.class).isEmpty()) continue; // already amended
                adminModel.getAdmin().addAndInitializeService(deployState, host, new AmendedService(host.getHost()));
            }
        }
Demonstrates how a model can be added at build time to amend another model.
This is useful is situations where the core Vespa config models needs to be
modified by third party code which follows the installed environment rather than
the application.

@author bratseth
config-model/src/test/java/com/yahoo/vespa/model/test/ModelAmendingTestCase.java