[Toy build testing] Stale=false scan throughput less than 20 scans per sec when KV ops rate is 12.5K sets per sec.

[Toy build testing-07/01] Stale=false scan throughput less than 20 scans per sec when KV ops rate is >10K.

Steps to reproduce:
1)Load 20M items and create and build 2i index on a single field.
2)Wait for index ready and start KV workload of 12.5K sets(updates) per sec.
3)Start cbindexperf workload for single row scans with concurrency 30 and sessionconsistency = true.
4)observe from server stats that stale=false scan rate is < 20 scans per sec.

https://s3.amazonaws.com/cb-customers/performance/15526/collectinfo-2015-07-02T003124-ns_1%40172.23.100.16.zip
https://s3.amazonaws.com/cb-customers/performance/15526/collectinfo-2015-07-02T003124-ns_1%40172.23.120.18.zip
https://s3.amazonaws.com/cb-customers/performance/15526/collectinfo-2015-07-02T003124-ns_1%40172.23.120.19.zip
https://s3.amazonaws.com/cb-customers/performance/15526/collectinfo-2015-07-02T003124-ns_1%40172.23.120.20.zip
https://s3.amazonaws.com/cb-customers/performance/15526/collectinfo-2015-07-02T003124-ns_1%40172.23.120.21.zip