Fix to the unit test failure in explicit TAP ack test.
Fix to the unit test failure in explicit TAP ack test.

Due to the fix (http://review.membase.org/#change,6404) to cleanning
up of 'dump' tap connections, the explicit TAP ack unit test failed.

The reason was that all the tap stats for a given named TAP
connection are reset after completing the dump operation.

Change-Id: I73ef32ce88134bf453f7f4dc602854f822005bac
Reviewed-on: http://review.membase.org/6505
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

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