private static Map<String, String> nameNodeRole(String value) {
    Map<String, String> params = new HashMap<>();
    params.put("desired_namenode_role", value);
    return params;
  }
Generates a list of UpgradeGroupHolder items that are used to execute either
an upgrade or a downgrade.

@param upgradePack
         the upgrade pack
@param context
         the context that wraps key fields required to perform an upgrade
@return the list of holders
ambari-server/src/main/java/org/apache/ambari/server/stack/upgrade/orchestrate/UpgradeHelper.java