Don't invoke notifyIOComplete directly upon receiving TAP bg item.
Don't invoke notifyIOComplete directly upon receiving TAP bg item.

This change is the rollback of http://review.membase.org/#change,6565

Change-Id: Ic668985621d04fa509ee8f88fbc4a1f9d78fb325
Reviewed-on: http://review.couchbase.org/6637
Reviewed-by: Bin Cui <ed18693fff32c00e22495f4877a3b901bed09041@gmail.com>
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

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