@Override
        public boolean apply(@Nullable String groupHost) {
          return clusterHosts.containsKey(groupHost);
        }
Register config groups for host group scoped configuration.
For each host group with configuration specified in the blueprint, a config group is created
and the hosts associated with the host group are assigned to the config group.
ambari-server/src/main/java/org/apache/ambari/server/topology/AmbariContext.java