String getIpAddress(String hostname) throws UnknownHostException {
    InetAddress inetAddress = InetAddress.getByName(hostname);
    return (inetAddress == null) ? null : inetAddress.getHostAddress();
  }
Constructor.
<p>
Given the Ambari {@link Configuration}, initializes the {@link KerberosName} class using
the <code>auth-to-local</code> rules from {@link AmbariKerberosAuthenticationProperties#getAuthToLocalRules()}.

@param configuration the Ambari configuration data
@param users         the Ambari users access object
ambari-server/src/main/java/org/apache/ambari/server/security/authentication/kerberos/AmbariProxiedUserDetailsService.java