private boolean isServiceInstalled(String serviceName) {
    return services.get(serviceName) != null;
  }
Gets desired configurations for the cluster.
@param allVersions specifies if all versions of the desired configurations to be returned
                   or only the active ones. It is expected that there is one and only one active
                   desired configuration per config type.
@param cachedConfigEntities retrieves cluster config entities from the cache if true, otherwise from the DB directly.
@return a map of type-to-configuration information.
ambari-server/src/main/java/org/apache/ambari/server/state/cluster/ClusterImpl.java