Make TestScannerAddToQueues less flaky.
Make TestScannerAddToQueues less flaky.

On my machine this test fails with surprising frequency because items
are removed from the queue before the test can see them.

bg451/cockroach,fengshao0907/cockroach,hassyma/cockroach,il9ue/cockroach,ajayaa/cockroach,linearb/cockroach,ngaut/cockroach,cockroachdb/cockroach,jamesgraves/cockroach,vivekmenezes/cockroach,yananzhi/cockroach,iqstack/cockroach,chrisseto/cockroach,SustainFund/cockroach,glycerine/cockroach,chrisseto/cockroach,Kevin-GuanJian/cockroach,veteranlu/cockroach,loucash/cockroach,il9ue/cockroach,slavau/cockroach,vaibhavarora/cockroach,cuongdo/cockroach,domluna/cockroach,paperstreet/cockroach,jamesgraves/cockroach,jgautheron/cockroach,fengshao0907/cockroach,glycerine/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,marcuswestin/cockroach,ajayaa/cockroach,iqstack/cockroach,vaibhavarora/cockroach,es-chow/cockroach,paperstreet/cockroach,vivekmenezes/cockroach,GokulSrinivas/cockroach,glycerine/cockroach,XisiHuang/cockroach,jgautheron/cockroach,XisiHuang/cockroach,bg451/cockroach,vivekmenezes/cockroach,yosiat/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,vivekmenezes/cockroach,jgautheron/cockroach,GokulSrinivas/cockroach,chrisseto/cockroach,veteranlu/cockroach,paperstreet/cockroach,petermattis/cockroach,il9ue/cockroach,yananzhi/cockroach,petermattis/cockroach,alunarbeach/cockroach,XisiHuang/cockroach,domluna/cockroach,hassyma/cockroach,ajayaa/cockroach,glycerine/cockroach,cockroachdb/cockroach,chrisseto/cockroach,yiixiansheng/cockroach,bg451/cockroach,abhishekgahlot/cockroach,alex/cockroach,nieyy/cockroach,veteranlu/cockroach,il9ue/cockroach,alex/cockroach,es-chow/cockroach,mbertschler/cockroach,arypurnomoz/cockroach,veteranlu/cockroach,mbonaci/cockroach,domluna/cockroach,slavau/cockroach,domluna/cockroach,hassyma/cockroach,jess-edwards/cockroach,Kevin-GuanJian/cockroach,ajayaa/cockroach,ngaut/cockroach,jmank88/cockroach,cockroachdb/cockroach,arjun4084346/cockroach,briceburg/cockroach,alunarbeach/cockroach,alex/cockroach,nieyy/cockroach,ngaut/cockroach,bg451/cockroach,jmank88/cockroach,freakynit/cockroach,yiixiansheng/cockroach,yananzhi/cockroach,arjun4084346/cockroach,cuongdo/cockroach,XisiHuang/cockroach,mbertschler/cockroach,freakynit/cockroach,nkhuyu/cockroach,cuongdo/cockroach,es-chow/cockroach,paperstreet/cockroach,arjun4084346/cockroach,alunarbeach/cockroach,jamesgraves/cockroach,ngaut/cockroach,veteranlu/cockroach,yosiat/cockroach,yananzhi/cockroach,sunya123/cockroach,marcuswestin/cockroach,petermattis/cockroach,arypurnomoz/cockroach,vaibhavarora/cockroach,GokulSrinivas/cockroach,fengshao0907/cockroach,veteranlu/cockroach,Abioy/cockroach,mbonaci/cockroach,nieyy/cockroach,ngaut/cockroach,SustainFund/cockroach,nieyy/cockroach,alex/cockroach,vaibhavarora/cockroach,fengshao0907/cockroach,yosiat/cockroach,alunarbeach/cockroach,il9ue/cockroach,yiixiansheng/cockroach,maxlang/cockroach,mbertschler/cockroach,alex/cockroach,loucash/cockroach,veteranlu/cockroach,abhishekgahlot/cockroach,glycerine/cockroach,linearb/cockroach,GokulSrinivas/cockroach,petermattis/cockroach,abhishekgahlot/cockroach,petermattis/cockroach,vaibhavarora/cockroach,maxlang/cockroach,bg451/cockroach,arypurnomoz/cockroach,sunya123/cockroach,nkhuyu/cockroach,il9ue/cockroach,sunya123/cockroach,sunya123/cockroach,vivekmenezes/cockroach,linearb/cockroach,maxlang/cockroach,cockroachdb/cockroach,paperstreet/cockroach,ajayaa/cockroach,c4pt0r/cockroach,marcuswestin/cockroach,fengshao0907/cockroach,slavau/cockroach,domluna/cockroach,Abioy/cockroach,arjun4084346/cockroach,Abioy/cockroach,cockroachdb/cockroach,yosiat/cockroach,glycerine/cockroach,nieyy/cockroach,mbertschler/cockroach,jess-edwards/cockroach,nkhuyu/cockroach,hassyma/cockroach,slavau/cockroach,freakynit/cockroach,ajayaa/cockroach,vaibhavarora/cockroach,jgautheron/cockroach,bg451/cockroach,bg451/cockroach,freakynit/cockroach,arjun4084346/cockroach,briceburg/cockroach,marcuswestin/cockroach,briceburg/cockroach,jamesgraves/cockroach,petermattis/cockroach,mbonaci/cockroach,maxlang/cockroach,jgautheron/cockroach,jmank88/cockroach,chrisseto/cockroach,c4pt0r/cockroach,mbertschler/cockroach,loucash/cockroach,cuongdo/cockroach,abhishekgahlot/cockroach,SustainFund/cockroach,linearb/cockroach,es-chow/cockroach,vivekmenezes/cockroach,yiixiansheng/cockroach,cockroachdb/cockroach,yananzhi/cockroach,iqstack/cockroach,jmank88/cockroach,sunya123/cockroach,linearb/cockroach,SustainFund/cockroach,jess-edwards/cockroach,Kevin-GuanJian/cockroach,arypurnomoz/cockroach,yiixiansheng/cockroach,Kevin-GuanJian/cockroach,cuongdo/cockroach,nieyy/cockroach,XisiHuang/cockroach,briceburg/cockroach,Abioy/cockroach,fengshao0907/cockroach,cuongdo/cockroach,nieyy/cockroach,maxlang/cockroach,arypurnomoz/cockroach,es-chow/cockroach,es-chow/cockroach,iqstack/cockroach,jgautheron/cockroach,jess-edwards/cockroach,yananzhi/cockroach,cockroachdb/cockroach,petermattis/cockroach,nkhuyu/cockroach,marcuswestin/cockroach,jamesgraves/cockroach,yosiat/cockroach,yananzhi/cockroach,maxlang/cockroach,hassyma/cockroach,marcuswestin/cockroach,jess-edwards/cockroach,jamesgraves/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,marcuswestin/cockroach,loucash/cockroach,maxlang/cockroach,es-chow/cockroach,GokulSrinivas/cockroach,alex/cockroach,il9ue/cockroach,maxlang/cockroach,mbonaci/cockroach,petermattis/cockroach,slavau/cockroach,mbonaci/cockroach,paperstreet/cockroach,freakynit/cockroach,sunya123/cockroach,Kevin-GuanJian/cockroach,freakynit/cockroach,arjun4084346/cockroach,alunarbeach/cockroach,c4pt0r/cockroach,slavau/cockroach,loucash/cockroach,ngaut/cockroach,Abioy/cockroach,arjun4084346/cockroach,arjun4084346/cockroach,linearb/cockroach,domluna/cockroach,sunya123/cockroach,abhishekgahlot/cockroach,jmank88/cockroach,jamesgraves/cockroach,loucash/cockroach,abhishekgahlot/cockroach,jmank88/cockroach,cuongdo/cockroach,chrisseto/cockroach,yosiat/cockroach,nieyy/cockroach,glycerine/cockroach,c4pt0r/cockroach,Kevin-GuanJian/cockroach,XisiHuang/cockroach,SustainFund/cockroach,mbertschler/cockroach,linearb/cockroach,alunarbeach/cockroach,jess-edwards/cockroach,mbertschler/cockroach,iqstack/cockroach,briceburg/cockroach,briceburg/cockroach,c4pt0r/cockroach,mbonaci/cockroach,glycerine/cockroach,c4pt0r/cockroach,marcuswestin/cockroach,jess-edwards/cockroach,yiixiansheng/cockroach,nkhuyu/cockroach,il9ue/cockroach,arypurnomoz/cockroach,hassyma/cockroach,Abioy/cockroach,iqstack/cockroach,paperstreet/cockroach,jmank88/cockroach,SustainFund/cockroach,ngaut/cockroach,domluna/cockroach,iqstack/cockroach,vivekmenezes/cockroach,sunya123/cockroach,cuongdo/cockroach,Kevin-GuanJian/cockroach,nkhuyu/cockroach,GokulSrinivas/cockroach