CRUNCH-642 Enable GroupingOptions for Distinct operations.

This fixes the existing call for numReducers as it was not working as
intended for non-memory PCollections due to using an invalid amount
of numReducers. To increase flexibility when using the API,
another call was added that allow to directly pass the GroupingOptions.

Signed-off-by: Josh Wills <jwills@apache.org>
3 files changed