Modify the return packet from help

* help should return "ok" if it succeeds (instead of ERR)
* help should return the same packet format as all of the other
  commands

Change-Id: I8c59e656ce6519816402e052ca9cbf45d204476d
Reviewed-on: http://review.couchbase.org/27926
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Trond Norbye <trond.norbye@gmail.com>