Added StreamingContext.getOrCreate to for automatic recovery, and added RecoverableNetworkWordCount example to use it.

Refactor DriverClient to be more Actor-based

Deduplicate Local and Cluster schedulers.

The code in LocalScheduler/LocalTaskSetManager was nearly identical
to the code in ClusterScheduler/ClusterTaskSetManager. The redundancy
made making updating the schedulers unnecessarily painful and error-
prone. This commit combines the two into a single TaskScheduler/
TaskSetManager.

Unfortunately the diff makes this change look much more invasive than it is -- TaskScheduler.scala is only superficially changed (names updated, overrides removed) from the old ClusterScheduler.scala, and the same with
TaskSetManager.scala.

Thanks @rxin for suggesting this change!

Clean up shuffle files once their metadata is gone

Previously, we would only clean the in-memory metadata for consolidated shuffle files.

Additionally, fixes a bug where the Metadata Cleaner was ignoring type-specific TTLs.

Change the order of CLASSPATH.

SPARK_TOOLS_JAR should be placed after CLASSPATH or at least after
SPARK_CLASSPATH.

If SPARK_TOOLS_JAR is placed before CLASSPATH, all assembled classes and
resources in spark-tools-assembly.jar beat those in CLASSPATH or
SPARK_CLASSPATH, which might be replaced by customized versions.

Show full stack trace and time taken in unit tests.

Refactored the streaming scheduler and added StreamingListener interface

- Refactored the streaming scheduler for cleaner code. Specifically, the JobManager was renamed to JobScheduler, as it does the actual scheduling of Spark jobs to the SparkContext. The earlier Scheduler was renamed to JobGenerator, as it actually generates the jobs from the DStreams. The JobScheduler starts the JobGenerator. Also, moved all the scheduler related code from spark.streaming to spark.streaming.scheduler package.
- Implemented the StreamingListener interface, similar to SparkListener. The streaming version of StatusReportListener prints the batch processing time statistics (for now). Added StreamingListernerSuite to test it.
- Refactored streaming TestSuiteBase for deduping code in the other streaming testsuites.

Added SPARK-968 implementation for review

Added SPARK-968 implementation for review