Update default etcd server to 3.3.15 for kubernetes 1.16
Update default etcd server to 3.3.15 for kubernetes 1.16

Change-Id: I68f1a5e5339d83077a1a9f312c4e6e33848886c5

Kubernetes-commit: 8fbfdf8267795d6960f9ac27f52affc6f29e7b76

kubernetes-nightly/sample-apiserver,kubernetes/sample-apiserver,kubernetes/sample-apiserver,kubernetes-nightly/sample-apiserver