Configurable volume mount options

I'm struggling with deploying a container with mounted volume. Container uses non-root user. I realized that Konlet mounts a device as root and doesn't let one to pass any custom mount [options ](https://github.com/GoogleCloudPlatform/konlet/blob/master/gce-containers-startup/volumes/volumes.go#L434). Because of permission issues the container doesn't work as expected.

Maybe I'm looking at wrong place. Maybe the problem should be solved in a different way, not on the Konlet side.

I'll appreciate any suggestions.

Start with gce-containers-startup/volumes/volumes.go around the mount handling linked in the issue. Trace how Konlet mounts devices as root and determine where custom mount options would need to be represented. Done means a non-root container can deploy with the required volume permissions and the behavior is covered by relevant tests or deployment verification.

Written by the indexing model from the issue text.