Cluster PUBLISH message: fix totlen count.

bulk_data field size was not removed from the count. It is not possible
to declare it simply as 'char bulk_data[]' since the structure is nested
into another structure.
fix benchmark memleak in loop mode
redis-benchmark: default num of requests is now 100000.

10000 completes in a too short time and may easily provide unreliable
figures because of tiny duration.