Merge pull request #65020 from detiber/etcd_grpc_gateway

Automatic merge from submit-queue (batch tested with PRs 64862, 65020). 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 - fix local etcd grpc gateway

**What this PR does / why we need it**:
etcd 3.2 uses the server certificate as the client cert for the grpc
gateway, this updates the generation of the etcd server certificate to
add client usage to resolve the issue.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes https://github.com/kubernetes/kubeadm/issues/910

**Release note**:
```release-note
NONE
```

cmd/kubeadm/app/phases/certs/certs.go

@@ -377,7 +377,7 @@ func NewEtcdServerCertAndKey(cfg *kubeadmapi.MasterConfiguration, caCert *x509.C
 	config := certutil.Config{
 		CommonName: cfg.NodeRegistration.Name,
 		AltNames:   *altNames,
-		Usages:     []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+		Usages:     []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
 	}
 	etcdServerCert, etcdServerKey, err := pkiutil.NewCertAndKey(caCert, caKey, config)
 	if err != nil {