public KerberosDetails getKerberosDetails()
      throws KerberosInvalidConfigurationException, AmbariException {
    return m_kerberosHelper.getKerberosDetails(m_cluster, null);
  }
Gets Kerberos information about a cluster. It should only be invoked if the
cluster's security type is set to {@link SecurityType#KERBEROS}, otherwise
it will throw an {@link AmbariException}.

@return the Kerberos related details of a cluster.
@throws KerberosInvalidConfigurationException
          if the {@code kerberos-env} or {@code krb5-conf}} configurations
          can't be parsed.
@throws AmbariException
          if the cluster is not Kerberized.
ambari-server/src/main/java/org/apache/ambari/server/stack/upgrade/orchestrate/UpgradeContext.java