MB-11779: Switch the engine context before we update the task log
MB-11779: Switch the engine context before we update the task log

If we don't do this then we lose 48 bytes from the bucket mem_used
each time the executor thread runs.

Change-Id: Iecf216e3c262573a3b36911f80f44b92851d2a5f
Reviewed-on: http://review.couchbase.org/40201
Tested-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

hisundar/ep-engine,membase/ep-engine,hisundar/ep-engine,sriganes/ep-engine,hisundar/ep-engine,daverigby/kv_engine,owendCB/ep-engine,daverigby/ep-engine,teligent-ru/ep-engine,owendCB/ep-engine,couchbase/ep-engine,teligent-ru/ep-engine,couchbase/ep-engine,sriganes/ep-engine,hisundar/ep-engine,teligent-ru/ep-engine,jimwwalker/ep-engine,membase/ep-engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/ep-engine,membase/ep-engine,couchbase/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,membase/ep-engine,jimwwalker/ep-engine,teligent-ru/ep-engine,couchbase/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,owendCB/ep-engine,sriganes/ep-engine,owendCB/ep-engine,sriganes/ep-engine,daverigby/kv_engine