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
I looked at CDH poms, and it looks like guava 11.0.2 is set in the parent pom, but the Spark pom just overrides the version. I don't think any of the existing packaged projects depend on both Hadoop and Spark, so it hasn't been an issue yet.