Add RowBatchQueue interface with an implementation backed by a std::queue

Add a RowBatchQueue interface with an implementation backed by a std::queue. Introducing a generic queue that can buffer RowBatch-es will help with the implementation of BufferedPlanRootSink. Rather than tie the BufferedPlanRootSink to a specific method of queuing row batches, we can use an interface. In future patches, a RowBatchQueue backed by a BufferedTupleStream can easily be switched out in BufferedPlanRootSink.

We should consider re-factoring the existing RowBatchQueue to use the new interface. The KRPC receiver does some buffering of RowBatch-es as well which might benefit from the new RowBatchQueue interface, and some more KRPC buffering might be added in IMPALA-6692.