SHDP-256 Add security config

- New options for configuration namespace controlling
  security, principals and keytab.
- schema changes for new 2.1 files
- User can login using a keytab file.
- Keeping test out of a way by forcing to use
  testGroup 'kerberos' because for now test
  assumes a specific kerberos setup which we
  don't have in CI.
Merge branch 'master' of https://github.com/spring-projects/spring-hadoop