Fix ClassCastException in JavaPairRDD.collectAsMap() (SPARK-1040)

This fixes [SPARK-1040](https://spark-project.atlassian.net/browse/SPARK-1040), an issue where JavaPairRDD.collectAsMap() could sometimes fail with ClassCastException.  I applied the same fix to the Spark Streaming Java APIs.  The commit message describes the fix in more detail.

I also increased the verbosity of JUnit test output under SBT to make it easier to verify that the Java tests are actually running.