public static void invalidateAffectedClusters() {
    for (Cluster cluster : affectedClusters.get()) {
      s_clusters.invalidate(cluster);
      affectedClusters.get().remove(cluster);
    }
  }
Provides utility methods to support operations retry
TODO injection as Guice singleon, static for now to avoid major modifications
ambari-server/src/main/java/org/apache/ambari/server/utils/RetryHelper.java