benchmark: make number of watcher streams configurable in watch-get
benchmark: make number of watcher streams configurable in watch-get

Each stream uses a client goroutine and a grpc stream; the setup causes
considerable client-side latency on the first get requests.

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