adding matrix factorization data generator
fixing formatting
Only reduce the number of cores once when removing an executor
Timeout zombie workers
milliseconds -> seconds in timeOutDeadWorkers logging
Moved handling of timed out workers within the Master actor
fixing formatting, style, and input
Merge pull request #776 from gingsmith/master

adding matrix factorization data generator
Merge pull request #769 from markhamstra/NegativeCores

SPARK-847 + SPARK-845: Zombie workers and negative cores