RFR 8200152: KerberosString should use UTF-8 by default

[Weijun Wang]

Please take a review of the code change and CSR at

   CSR: https://bugs.openjdk.java.net/browse/JDK-8200153
   webrev: http://cr.openjdk.java.net/~weijun/8200152/webrev.00/

Thanks
Max