Gated modifiers ignore device requests by volume mounts

[elezar]

The gated modifiers used to add support for GDS, Mofed, and CUDA Forward Comatibility only check the NVIDIA_VISIBLE_DEVICES envvar to determine whether GPUs are requested and modifications should be made. This means that use cases where volume mounts are used to request devices (e.g. when using the GPU Device Plugin) are not supported.

We need to update the check here to include other request mechanism:

	if devices := image.VisibleDevicesFromEnvVar(); len(devices) == 0 {
		logger.Infof("No modification required; no devices requested")
		return nil, nil
	}