Implement kinit command execution facility in Java by leveraging Apache Kerby

The kinit command is configured and invoked for obtaining and renewing tickets in Hadoop. There will be some benefits to implement the facility by leveraging the Kerby KrbClient API:
1. Resolve the hard dependency to MIT Kerberos client package;
2. Pure in Java, no need to configure and set up any runnable environment, easy to support on various platforms, easy to maintain and test.

This proposes to do the change with a prototype patch for the review and discussion. Welcome your feedback. Thanks.