benchmark: fix watch command
benchmark: fix watch command

Fix https://github.com/coreos/etcd/issues/5099.

jlamillan/etcd,endocode/etcd,joshix/etcd,glycerine/etcd,cockroachdb/etcd,bluebreezecf/etcd,tguangch/etcd,wantonsolutions/dinv-etcd,chipironcin/etcd,nekto0n/etcd,ajityagaty/etcd,insequent/etcd,sebrandon1/etcd,plasticbox/etcd,luxas/etcd,ravigadde/etcd,rchicoli/etcd,zaphod-concur/etcd,mkumatag/etcd,insequent/etcd,swingbach/etcd,li-ang/etcd,ktateish/etcd,xiang90/etcd,armstrongli/etcd,lumjjb/etcd,dnaeon/etcd,a-robinson/etcd,lumjjb/etcd,YuleiXiao/etcd,rnaveiras/etcd,glycerine/etcd,heyitsanthony/etcd,sofuture/etcd,hongchaodeng/etcd,visheshnp/etcd,akauppi/etcd,mickep76/etcd,lorneli/etcd,sinsharat/etcd,mqliang/etcd,ravigadde/etcd,rnaveiras/etcd,jlamillan/etcd,dannysauer/etcd,coreos/etcd,westhood/etcd,fanminshi/etcd,StorReduce/etcd,nekto0n/etcd,bdarnell/etcd,joshix/etcd,wantonsolutions/dinv-etcd,westhood/etcd,tguangch/etcd,armstrongli/etcd,CrazyJvm/etcd,etcd-io/etcd,cockroachdb/etcd,dnaeon/etcd,sebrandon1/etcd,luxas/etcd,OyTao/etcd_learning,lorneli/etcd,StorReduce/etcd,ajityagaty/etcd,coreos/etcd,mqliang/etcd,gyuho/etcd,mkumatag/etcd,endocode/etcd,xiang90/etcd,sinsharat/etcd,yudai/etcd,YuleiXiao/etcd,purpleidea/etcd,chipironcin/etcd,handsomesun/etcd,glevand/coreos--etcd,gyuho/etcd,li-ang/etcd,jonboulle/etcd,glevand/coreos--etcd,bdarnell/etcd,purpleidea/etcd,yudai/etcd,vimalk78/etcd,ktateish/etcd,handsomesun/etcd,mqliang/etcd,linuxcer/etcd,bluebreezecf/etcd,linuxcer/etcd,OyTao/etcd_learning,whuwxl/etcd,wantonsolutions/dinv-etcd,plasticbox/etcd,etcd-io/etcd,heyitsanthony/etcd,swingbach/etcd,whuwxl/etcd,visheshnp/etcd,jonboulle/etcd,mkumatag/etcd,fanminshi/etcd,a-robinson/etcd,rchicoli/etcd,zaphod-concur/etcd,akauppi/etcd,rnaveiras/etcd,etcd-io/etcd,ajityagaty/etcd,CrazyJvm/etcd,hongchaodeng/etcd,qqsun8819/etcd,mickep76/etcd,dannysauer/etcd,sofuture/etcd,qqsun8819/etcd,vimalk78/etcd