Take advantage of `csi_secret` in CSI 1.0

[saad-ali]

CSI 1.0 decorates senstive fields with csi_secret. Let's take advantage of this feature to programmatically ensure no sensitive fields are ever logged by this side car container.

[pohly]

PR open against external-provisioner: kubernetes-csi/external-provisioner#171

Needs to be reviewed there and then could be copied into external-snapshotter.