tune and fix rebalance test
tune and fix rebalance test

PaintScratcher/perfrunner,EricACooper/perfrunner,EricACooper/perfrunner,EricACooper/perfrunner,couchbase/perfrunner,couchbase/perfrunner,mikewied/perfrunner,couchbase/perfrunner,vmx/perfrunner,EricACooper/perfrunner,vmx/perfrunner,couchbase/perfrunner,couchbase/perfrunner,PaintScratcher/perfrunner,pavel-paulau/perfrunner,dkao-cb/perfrunner,dkao-cb/perfrunner,thomas-couchbase/perfrunner,couchbase/perfrunner,pavel-paulau/perfrunner,hsharsha/perfrunner,mikewied/perfrunner,thomas-couchbase/perfrunner,hsharsha/perfrunner,pavel-paulau/perfrunner,pavel-paulau/perfrunner,pavel-paulau/perfrunner