Feature abstraction

Hi, This PR should allow this cookbook to work out of the box by adding some default attributes to allow it to work out of the box, and be a bit more flexible.

* Set java attributes to install a newer version of oracle jre via rpm
* Add a `cluster_name` to the kitchen tests
* Allow for a cookbook other than the open source java cookbook to run
* Allow for other yum repos to be used to install `dsc20`

Also, the `README` was updated to reflect the new attributes and also addresses https://github.com/michaelklishin/cassandra-chef-cookbook/issues/100