Allow CSR that contains either IP or DNS as SANs

In some environments, kubelet may only send IP addresses or DNS
address as SANs in CSR. For example, kubelet which starts with
`--hostname-override=IP_ADDRRES` only sends IP addresses.
So we should allow this CSR.

pkg/controller/certificatesigningrequest/helpers.go

@@ -73,7 +73,7 @@ func isNodeServingCert(csr *capi.CertificateSigningRequest, x509cr *x509.Certifi
 		klog.Warningf("Org does not match: %s", x509cr.Subject.Organization)
 		return false
 	}
-	if (len(x509cr.DNSNames) < 1) || (len(x509cr.IPAddresses) < 1) {
+	if (len(x509cr.DNSNames) < 1) && (len(x509cr.IPAddresses) < 1) {
 		return false
 	}
 	if !hasExactUsages(csr, kubeletServerUsages) {