protected String getProperty(UpgradeCheckRequest request, String configType, String propertyName)
      throws AmbariException {
    final String clusterName = request.getClusterName();
    final Cluster cluster = clustersProvider.get().getCluster(clusterName);
    final Map<String, DesiredConfig> desiredConfigs = cluster.getDesiredConfigs();
    final DesiredConfig desiredConfig = desiredConfigs.get(configType);

    if (null == desiredConfig) {
      return null;
    }

    final Config config = cluster.getConfig(configType, desiredConfig.getTag());

    Map<String, String> properties = config.getProperties();
    return properties.get(propertyName);
  }
Gets a cluster configuration property if it exists, or {@code null}
otherwise.

@param request
         the request (not {@code null}).
@param configType
         the configuration type, such as {@code hdfs-site} (not
         {@code null}).
@param propertyName
         the name of the property (not {@code null}).
@return the property value or {@code null} if not found.
@throws AmbariException
ambari-server/src/main/java/org/apache/ambari/server/checks/ClusterCheck.java