etcd: Pass through the namespace

This is a bit tricky, and we should nuke and redo some of this API. The
sneaky bit has to do with whether we've already added the namespace
magic into our etcd client or not.

etcd/interfaces/client.go

@@ -66,6 +66,8 @@ type WatcherInfo struct {
 // EmbdEtcd.MakeClient and client.Simple implement this.
 type Client interface {
 	GetClient() *etcd.Client
+	GetNamespace() string
+
 	Set(ctx context.Context, key, value string, opts ...etcd.OpOption) error
 	Get(ctx context.Context, path string, opts ...etcd.OpOption) (map[string]string, error)
 	Del(ctx context.Context, path string, opts ...etcd.OpOption) (int64, error)