keystone-auth webhook causes failure in Magnum clusters

[waipeng]

While testing out new versions of this chart, I found that #91 may have broken how Magnum uses this chart via the magnum-capi-helm driver. Using mostly defaults for the cluster template, creating a Magnum cluster using the latest driver code and v0.5.0 of this chart results in a cluster that cannot complete creating. Further investigations shows:

root@jake-7g23skeiu6mk-control-plane-d304fe4f-c2dtm:~# kubectl get clusterrolebindings cluster-admin
Error from server (InternalError): an error on the server ("Internal Server Error: \"/apis/rbac.authorization.k8s.io/v1/clusterrolebindings/cluster-admin\": Post \"https://127.0.0.1:8443/webhook?timeout=30s\": dial tcp 127.0.0.1:8443: connect: connection refused") has prevented the request from succeeding (get clusterrolebindings.rbac.authorization.k8s.io cluster-admin)

The URL https://127.0.0.1:8443 is the defaults from stackhpc@2bfe594#diff-69445aa57c2a517f040e86a387853612efaacca40edb3ba2988de35a859dcf38R399

This happened because magnum-capi-helm driver defaults keystone-auth to True [1]. Perhaps more testing needs to be done between magnum-capi-helm driver and this?

[1] https://github.com/stackhpc/magnum-capi-helm/blob/v0.12.0/magnum_capi_helm/driver.py#L587