private HostResource addNewHost(HostSpec hostSpec) {
        String hostname = checkHostname(hostSpec.hostname());
        HostResource hostResource = new HostResource(Host.createHost(this, hostname), hostSpec);
        hostSpec.networkPorts().ifPresent(np -> hostResource.ports().addNetworkPorts(np));
        hostname2host.put(hostname, hostResource);
        return hostResource;
    }
The parent node for all Host instances, and thus accessible
to enable services to get their Host.

@author gjoranv
config-model/src/main/java/com/yahoo/vespa/model/HostSystem.java