Changelog: Update changelog for 3.4.21
Changelog: Update changelog for 3.4.21

Signed-off-by: Benjamin Wang <a1713d12b1b05630690f22cadfd282d625d8acb2@vmware.com>

ajityagaty/etcd,etcd-io/etcd,etcd-io/etcd,ajityagaty/etcd,ajityagaty/etcd,etcd-io/etcd