Synchronize UPRProducer::handleResponse API through the lock.
Synchronize UPRProducer::handleResponse API through the lock.

Change-Id: I782d8e0c126a23174d50eb89c628f91d791dbe39
Reviewed-on: http://review.couchbase.org/38995
Reviewed-by: abhinav dangeti <d73ef2279de6577f7bf081737ee47554bbb7dc82@couchbase.com>
Tested-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

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