revise worker helper and add more logging events
revise worker helper and add more logging events

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