Eliminate extra memory usage when shuffle file consolidation is disabled

Otherwise, we see SPARK-946 even when shuffle file consolidation is disabled.
Fixing SPARK-946 is still forthcoming.
Use flag instead of name check.
Merge pull request #115 from aarondav/shuffle-fix

Eliminate extra memory usage when shuffle file consolidation is disabled

Otherwise, we see SPARK-946 even when shuffle file consolidation is disabled.
Fixing SPARK-946 is still forthcoming.