When authenticating openshift-install with the gcloud cli, rather than using a service account key file, the installer will throw an error because https://github.com/openshift/installer/blob/master/pkg/asset/machines/gcp/machines.go#L170-L178 ALWAYS expects to extract a service account to passthrough to nodes in XPN installs. 

An alternative approach would be to handle the lack of service account without error, and allow the required service accounts to passed in through another mechanism.

1.Create install config for gcp xpn install
2.Authenticate installer without service account key file (either gcloud cli auth or through a VM).
3.