pkg/ioutil: add "FlushN"
pkg/ioutil: add "FlushN"

Signed-off-by: Gyuho Lee <0fbd30d364d71722b926950b451cecd97b54fc29@amazon.com>

rnaveiras/etcd,mqliang/etcd,mqliang/etcd,gyuho/etcd,mkumatag/etcd,etcd-io/etcd,etcd-io/etcd,ajityagaty/etcd,dannysauer/etcd,mkumatag/etcd,ajityagaty/etcd,etcd-io/etcd,li-ang/etcd,li-ang/etcd,mkumatag/etcd,cockroachdb/etcd,mqliang/etcd,gyuho/etcd,cockroachdb/etcd,coreos/etcd,rnaveiras/etcd,rnaveiras/etcd,dannysauer/etcd,ajityagaty/etcd,coreos/etcd