cbc-pillowfight features that enable DGM workloads

-D  Specify if testing with data greater than memory
   (default false) (--data-greater-than-memory)
-n  Skip populating (default false) (--no-population)
    The first option is needed for rapidly generating workload
    where the data is much greater than memory
    The second option allows the tester to directly skip to the
    workload phase if the data is already loaded.
    If this is not there, then cbc-pillowfight ends up loading
    data once again, and this can take a long time if we are in
    DGM mode!
-w  wait time in seconds for DGM operations to complete
    (default 10) (--wait-for-op)
Change-Id: Iaf372442428201c32d0f8ec1ddb7002f8899d4c4
Reviewed-on: http://review.couchbase.org/30637
Tested-by: Sundararaman Sridharan <sundar.sridharan@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>