use the same base report and only customize iterator

irrelevant charts will be filtered out in any case

Change-Id: I2f91a97350dc81d1c5b71e8b5da14b8621bc2dfc
Reviewed-on: http://review.couchbase.org/30845
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>