Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

kubeadm: When etcd is listening on all interfaces, set the etcd probe to use loopback

**What this PR does / why we need it**:
When constructing the etcd liveness probe, if the user passes an IPv4 or IPv6 address,
we set the `etcdctl` liveness probe to use the respective IPv4 or IPv6 loopback address for `--endpoints`.

The etcd probe is now always formatted with the https:// protocol and square brackets around the IP (required for IPv6 / compatible with IPv4).

`::1` is now also included in the etcd serving cert SAN by default.

/kind bug
/area kubeadm
/area etcd
/priority important-soon

/sig cluster-lifecycle
/assign @fabriziopandini

**Which issue(s) this PR fixes**
Fixes https://github.com/kubernetes/kubeadm/issues/882

**Special notes for your reviewer**:
```bash
root@vagrant:~# /vagrant/bin/882_kubeadm init --config /dev/stdin << EOF |& tail -n5
etcd:
  extraArgs:
    listen-client-urls: https://[::]:2379
EOF
I0603 19:52:15.666594   24743 tlsbootstrap.go:50] [bootstraptoken] configured RBAC rules to allow Node Bootstrap tokens to post CSRs in order for nodes to get long term certificate credentials
I0603 19:52:15.671424   24743 tlsbootstrap.go:72] [bootstraptoken] configured RBAC rules to allow the csrapprover controller automatically approve CSRs from a Node Bootstrap Token
I0603 19:52:15.674607   24743 tlsbootstrap.go:95] [bootstraptoken] configured RBAC rules to allow certificate rotation for all node client certificates in the cluster
I0603 19:52:15.677551   24743 clusterinfo.go:43] [bootstraptoken] creating the "cluster-info" ConfigMap in the "kube-public" namespace
[addons] Applied essential addon: CoreDNS
[addons] Applied essential addon: kube-proxy
root@vagrant:~# cat /etc/kubernetes/manifests/etcd.yaml |grep -C4 listen
spec:
  containers:
  - command:
    - etcd
    - --listen-client-urls=https://[::]:2379
    - --advertise-client-urls=https://127.0.0.1:2379
    - --cert-file=/etc/kubernetes/pki/etcd/server.crt
    - --client-cert-auth=true
    - --data-dir=/var/lib/etcd
root@vagrant:~# cat /etc/kubernetes/manifests/etcd.yaml |grep -C4 etcdctl
      exec:
        command:
        - /bin/sh
        - -ec
        - ETCDCTL_API=3 etcdctl --endpoints=https://[::1]:2379 --cacert=/etc/kubernetes/pki/etcd/ca.crt
          --cert=/etc/kubernetes/pki/etcd/healthcheck-client.crt --key=/etc/kubernetes/pki/etcd/healthcheck-client.key
          get foo
      failureThreshold: 8
      initialDelaySeconds: 15
```

**Release note**:
```release-note
kubeadm now configures the etcd liveness probe correctly when etcd is listening on all interfaces
```