This patch re-adds a test which was removed in 9ebb44f8ab due to a Java 6 compatibility issue. We now use Guava's `Iterators.emptyIterator()` in place of `Collections.emptyIterator()`, which isn't present in all Java 6 versions.
Author: Josh Rosen <joshrosen@databricks.com>
Closes#6298 from JoshRosen/SPARK-7719-fix-java-6-test-code and squashes the following commits:
5c9bd85 [Josh Rosen] Re-add UnsafeShuffleWriterSuite.emptyIterator() test which was removed due to Java 6 issue
(cherry picked from commit 5196efff53)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>