CDK-515: Added tests for Spark jobs reading from/writing to Datasets.

 * Added spark-core_2.10 under dependency management
 * Implemented tests that use FileSystemDataset and HBaseDataset
Since I upped the minimum Spark version to 1.0.0, I got the ability to use the saveAsNewAPIHadoopDataset() method instead of the saveAsNewAPIHadoopFile(). However, in order to use the new method, the configuration object you pass in must have the Hadoop output format configured and we only do that in DatasetKeyOutputFormat.configure(Job).