pillowfight: Option renaming

- Rename the confusing '--iterations' option to '--batch-size'. The
  option controls the batch size, not how many times the workload
  iterates.

- Hide the `-Q` or `--num-instances` parameter. It is confusing and
  doesn't really gain much. The only thing that should matter in a
  threaded workload where each instance is locked is the number of threads
  executing

- Add the `--num-cycles` parameter to indicate how many iterations (in
  the real sense) the loop should run.

Note that the old options are still supported, but are left undocumented

Change-Id: Idc4f2c9a65aed7cbdda8cbc942f96852f9a58aa2
Reviewed-on: http://review.couchbase.org/38687
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>