etcdhttp: add metrics.go for metrics, health handler
etcdhttp: add metrics.go for metrics, health handler

Signed-off-by: Gyu-Ho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

mqliang/etcd,joshix/etcd,visheshnp/etcd,a-robinson/etcd,vimalk78/etcd,YuleiXiao/etcd,gyuho/etcd,lorneli/etcd,lorneli/etcd,mqliang/etcd,dannysauer/etcd,glevand/coreos--etcd,rnaveiras/etcd,bdarnell/etcd,a-robinson/etcd,rnaveiras/etcd,xiang90/etcd,whuwxl/etcd,ajityagaty/etcd,etcd-io/etcd,visheshnp/etcd,bluebreezecf/etcd,bdarnell/etcd,li-ang/etcd,sebrandon1/etcd,bluebreezecf/etcd,fanminshi/etcd,ajityagaty/etcd,cockroachdb/etcd,ajityagaty/etcd,mkumatag/etcd,sinsharat/etcd,heyitsanthony/etcd,fanminshi/etcd,mkumatag/etcd,sinsharat/etcd,sebrandon1/etcd,mqliang/etcd,mkumatag/etcd,akauppi/etcd,etcd-io/etcd,gyuho/etcd,coreos/etcd,YuleiXiao/etcd,joshix/etcd,whuwxl/etcd,xiang90/etcd,mickep76/etcd,coreos/etcd,li-ang/etcd,cockroachdb/etcd,heyitsanthony/etcd,vimalk78/etcd,akauppi/etcd,glevand/coreos--etcd,mickep76/etcd,rnaveiras/etcd,etcd-io/etcd,dannysauer/etcd