Reduce Processor can parallelize I/O/Processor initialization

Reported by gopalv. Reduce initialization can take a fair amount of time after shuffle is complete - depending on how expensive the Reduce initialization is.

Quote from Gopal's investigation
1.6 seconds is spent in ReflectionUtils.newInstance() -> ReflectionUtils.setConf() of which 1.2 seconds is Utilities.getMapRedWork().