cert-manager: fix DNS for http01 k0 splitdns

Change-Id: I73847daec9796cb891cf2fe58c2633c5fa768861
diff --git a/cluster/kube/lib/cert-manager.libsonnet b/cluster/kube/lib/cert-manager.libsonnet
index 93b9357..f10768f 100644
--- a/cluster/kube/lib/cert-manager.libsonnet
+++ b/cluster/kube/lib/cert-manager.libsonnet
@@ -451,6 +451,10 @@
                     template+: {
                         spec+: {
                             serviceAccountName: env.sas.certmanager.metadata.name,
+                            dnsPolicy: "None",
+                            dnsConfig: {
+                               nameservers: ["8.8.8.8"],
+                            },
                             containers_: {
                                 webhook: kube.Container("cert-manager") {
                                     image: "quay.io/jetstack/cert-manager-controller:" + cfg.version,