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
It's a shame that we need to basically duplicate our tests for both filesystem and HBase implementations. This is of wider scope than this change, but I'd like to work out a way to reduce duplication. After all, one of the promises of Kite is that you can use the same API for different storage backends.