Feature/krb import

Welcome to the Kerberos support for Continuuity Loom... this is a huge branch, which started with just a cookbook import. This branch has quite a bit of code changes in it. I will only highlight a few:

- [x] `krb5` cookbook import from atomic-penguin/cookbook-krb5#4
- [x] `krb_utils` cookbook, created by @wolf31o2
- [x] `attributes/krb5.rb` in `hadoop_wrapper` cookbook, to setup Hadoop settings
- [x] `recipes/jce.rb` in `hadoop_wrapper` cookbook, to download JCE from Oracle
- [x] `kerberos-client` and `kerberos-master` service JSON ( Issue #94 )
- [x] `kerberos-singlenode` clustertemplate JSON ( Issue #94 )
- [x] `recipes/kerberos_init.rb` in `hadoop_wrapper` cookbook to run `krb5_utils` to create keytab files

With this, one should be able to get a secure Hadoop cluster ( Issue #95 ) with only a few additional JSON attributes in their clustertemplate, for their default Kerberos realm and the KDC/kadmind server addresses.