etcdserver: refactor non-blocking check for sync tests
etcdserver: refactor non-blocking check for sync tests

to make it much more reliable and avoid false errors.

SivagnanamCiena/etcd,betawaffle/etcd,snailwalker/etcd,lorneli/etcd,lzbgt/etcd,honeyqa/etcd,rnaveiras/etcd,Winslett/etcd,kkaneda/etcd,freeloop1114/etcd,yifan-gu/etcd,plasticbox/etcd,jravetch/etcd,jeremyeder/etcd,gityf/etcd,jonboulle/etcd,junxu/etcd,bspline/etcd,tempbottle/etcd,whuwxl/etcd,xueshanf/etcd,yudai/etcd,mischief/etcd,iamqizhao/etcd,endocode/etcd,axingblog/etcd,purpleidea/etcd,svdata/etcd,li-ang/etcd,cognusion/etcd,whuwxl/etcd,sayden/etcd,jefby/etcd,sayden/etcd,njharman/etcd,handsomesun/etcd,njharman/etcd,Timer/etcd,joshix/etcd,glensc/etcd,sinsharat/etcd,fasaxc/etcd,youxidev/etcd,kingland/etcd,fgbreel/etcd,es-chow/etcd,insequent/etcd,gouyang/etcd,chenbaihu/etcd,openedbox/etcd,honeyqa/etcd,coreos/etcd,tamird/etcd,YuleiXiao/etcd,crandles/etcd,insequent/etcd,xdlinear/etcd,chipironcin/etcd,gouyang/etcd,gae123/etcd,combk8s/etcd,sebschrader/etcd,StorReduce/etcd,armstrongli/etcd,asim/etcd,swingbach/etcd,joshix/etcd,lorneli/etcd,visheshnp/etcd,glensc/etcd,bluebreezecf/etcd,jlamillan/etcd,chai2010-playground/etcd,etcd-io/etcd,sofuture/etcd,siddontang/etcd,hzy001/etcd,giantswarm/etcd,xdlinear/etcd,hpcloud/etcd,luxas/etcd,etcd-io/etcd,delkyd/etcd,raoofm/etcd,onlyjob/etcd,armstrongli/etcd,ajityagaty/etcd,tempbottle/etcd,xychu/etcd,cognusion/etcd,msanterre/etcd,tamird/etcd,ktateish/etcd,pengzj/etcd,yichengq/etcd,StorReduce/etcd,tguangch/etcd,oscarrr110/etcd,snailwalker/etcd,elimisteve/etcd,achanda/etcd,mickep76/etcd,fanminshi/etcd,yyljlyy/etcd,mqliang/etcd,mgoelzer/etcd-fork2,princeqjzh/etcd,bdarnell/etcd,QuantiumTechnology/etcd,freeloop1114/etcd,xueshanf/etcd,Timer/etcd,es-chow/etcd,asim/etcd,shafreeck/etcd,gyuho/etcd,dalanlan/etcd,kkaneda/etcd,xiang90/etcd,nekto0n/etcd,polvi/etcd,beni55/etcd,akauppi/etcd,elimisteve/etcd,offscale/etcd,gosharplite/etcd,rchicoli/etcd,mkumatag/etcd,tangkun75/etcd,msanterre/etcd,jeremyeder/etcd,mischief/etcd,shakefu/etcd,QuantiumTechnology/etcd,gyuho/etcd,yyljlyy/etcd,rchicoli/etcd,mwitkow/etcd,a-robinson/etcd,visheshnp/etcd,nkhare/etcd,sebrandon1/etcd,chai2010/etcd,jravetch/etcd,xiang90/etcd,mwitkow/etcd,HideoYamauchi/etcd,jmptrader/etcd,akauppi/etcd,nkhare/etcd,mike-lerch/etcd,mitake/etcd,fasaxc/etcd,hroyrh/etcd,hpcloud/etcd,dnaeon/etcd,Eagle-X/etcd,Yhgenomics/etcd,jlamillan/etcd,gtank/etcd,hzy001/etcd,improbable-io/etcd,youxidev/etcd,OyTao/etcd_learning,xychu/etcd,ylong/etcd,ylong/etcd,yifan-gu/etcd,bakins/etcd,svdata/etcd,zaphod-concur/etcd,siddontang/etcd,rnaveiras/etcd,cchamplin/etcd,vimalk78/etcd,wfxiang08/etcd,heyitsanthony/etcd,xebitstudios/etcd,purpleidea/etcd,Eagle-X/etcd,qiaochao911/etcd,devfreesg/etcd,ravigadde/etcd,YuleiXiao/etcd,princeqjzh/etcd,wantonsolutions/dinv-etcd,beni55/etcd,chenbaihu/etcd,mickep76/etcd,chai2010/etcd,onlyjob/etcd,glycerine/etcd,swingbach/etcd,Winslett/etcd,sofuture/etcd,wfxiang08/etcd,steveeJ/etcd,handsomesun/etcd,dterei/etcd,junxu/etcd,qqsun8819/etcd,nieanan/etcd,shawnps/etcd,delkyd/etcd,westhood/etcd,ecnahc515/etcd,jchauncey/etcd,justintung/etcd,mkumatag/etcd,iamqizhao/etcd,shakefu/etcd,robszumski/etcd,nieanan/etcd,pengzj/etcd,endocode/etcd,raoofm/etcd,pauldallen/etcd,plasticbox/etcd,qqsun8819/etcd,wowsoso/etcd,westhood/etcd,achanda/etcd,sebschrader/etcd,mike-lerch/etcd,oscarrr110/etcd,li-ang/etcd,CrazyJvm/etcd,spacejam/etcd,etcd-io/etcd,dannysauer/etcd,njucslqq/etcd,njucslqq/etcd,barakmich/etcd,imzhulei/etcd,robszumski/etcd,xebitstudios/etcd,arthurcolle/etcd,ktateish/etcd,ajityagaty/etcd,dannysauer/etcd,jmptrader/etcd,jchauncey/etcd,lumjjb/etcd,hongchaodeng/etcd,improbable-io/etcd,bakins/etcd,hongchaodeng/etcd,luxas/etcd,glevand/coreos--etcd,fgbreel/etcd,glycerine/etcd,arthurcolle/etcd,SivagnanamCiena/etcd,barakmich/etcd,devfreesg/etcd,chipironcin/etcd,offscale/etcd,wantonsolutions/dinv-etcd,sinsharat/etcd,hroyrh/etcd,pauldallen/etcd,qiaochao911/etcd,spacejam/etcd,shafreeck/etcd,HideoYamauchi/etcd,cchamplin/etcd,dnaeon/etcd,linuxcer/etcd,jefby/etcd,fanminshi/etcd,ravigadde/etcd,justintung/etcd,lumjjb/etcd,heyitsanthony/etcd,sebrandon1/etcd,glevand/coreos--etcd,steveeJ/etcd,bspline/etcd,rnaveiras/etcd,wowsoso/etcd,cockroachdb/etcd,giantswarm/etcd,a-robinson/etcd,dalanlan/etcd,bdarnell/etcd,jonboulle/etcd,wantonsolutions/dinv-etcd,axingblog/etcd,csuideal/etcd,nekto0n/etcd,mqliang/etcd,ajityagaty/etcd,olark/etcd,chai2010-playground/etcd,mitake/etcd,CrazyJvm/etcd,gtank/etcd,betawaffle/etcd,mwitkow-io/etcd,openedbox/etcd,vimalk78/etcd,Yhgenomics/etcd,coreos/etcd,TheHippo/etcd,linuxcer/etcd,buaazp/etcd,tangkun75/etcd,combk8s/etcd,yudai/etcd,polvi/etcd,gosharplite/etcd,mgoelzer/etcd-fork2,gityf/etcd,dterei/etcd,shawnps/etcd,gae123/etcd,yichengq/etcd,ecnahc515/etcd,hongbinz/etcd,mqliang/etcd,zaphod-concur/etcd,tguangch/etcd,mwitkow-io/etcd,insionng/etcd,olark/etcd,imzhulei/etcd,OyTao/etcd_learning,csuideal/etcd,kingland/etcd,TheHippo/etcd,bluebreezecf/etcd,insionng/etcd,fasaxc/etcd,buaazp/etcd,hongbinz/etcd,crandles/etcd,lzbgt/etcd,cockroachdb/etcd,mkumatag/etcd