func NewLease(l clientv3.Lease, prefix string) clientv3.Lease {
	return &leasePrefix{l, []byte(prefix)}
}
NewLease wraps a Lease interface to filter for only keys with a prefix
and remove that prefix when fetching attached keys through TimeToLive.
package namespace
import (
	"bytes"
	"golang.org/x/net/context"
	"github.com/coreos/etcd/clientv3"
)
type leasePrefix struct {
	clientv3.Lease
	pfx []byte
}