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
For new stuff like this, let's go to latest stable upstream release, currently spark-1.0.1. I doubt spark on cdh4 is usable or supportable, e.g. wrt to the spark-1.0 API changes.