CBQE-1155 Fix issue in stats wait

ep_flusher_todo stat has changed on the server side.
As per new behavior, this stat can be ignored.
Eventually this stat will be removed.

Change-Id: I1c95d10f374ad7cbde162ffec31d545cd2f10fce
Reviewed-on: http://review.couchbase.org/25510
Reviewed-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>
Tested-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>