Make reduce side join work for all join queries [Spark Branch]

Regardless all these join related optimizations such as map join, bucket join, skewed join, etc, reduce side join is the fallback. That means, if a join query wasn't taken care of by any of the optimization, it should work with reduce side join (might in a less optimal fashion).

It's found that this isn't case at the moment. For instance, auto_sortmerge_join_1.q failed to execute on Spark.