pillowfight: timestamp messages in timings mode

Change-Id: I6ab6648535a88ad659a73f353099041ab3a9aae2
Reviewed-on: http://review.couchbase.org/26773
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>