WIP: Added consumer queue rerouting

This allows the application to consume from multiple topic+partitions
with a single rd_kafka_consume*() call, instead of one such
call per topic+partition.
Added consumer queue rerouting

This allows the application to consume from multiple topic+partitions
with a single rd_kafka_consume*() call, instead of one such
call per topic+partition.
Added "unique" test ids for message validation
Added RD_KAFKA_OFFSET_TAIL(cnt) to start consuming 'cnt' messages from end.

An application can now easily consume the last 'cnt' messages from a partition.
Added produce->consume test (produce batch, consumer queues, TAIL)
produce_batch(): Fixed race condition when cluster comes up

If rdkafka is connecting to the cluster for the first time at the same
time as a larger batch is produced the message batch may end up
stuck in the Unassigned partition queue.