Add devRoot option to CDI api

A driverRoot defines both the driver library root and the
root for device nodes. In the case of preinstalled drivers or
the driver container, these are equal, but in cases such as GKE
they do not match. In this case, drivers are extracted to a folder
and devices exist at the root /.

The changes here add a devRoot option to the nvcdi API that allows the
parent of /dev to be specified explicitly.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

pkg/nvcdi/lib.go

@@ -44,6 +44,7 @@ type nvcdilib struct {
 	devicelib          device.Interface
 	deviceNamer        DeviceNamer
 	driverRoot         string
+	devRoot            string
 	nvidiaCTKPath      string
 	librarySearchPaths []string
 
@@ -76,6 +77,9 @@ func New(opts ...Option) (Interface, error) {
 	if l.driverRoot == "" {
 		l.driverRoot = "/"
 	}
+	if l.devRoot == "" {
+		l.devRoot = l.driverRoot
+	}
 	if l.nvidiaCTKPath == "" {
 		l.nvidiaCTKPath = "/usr/bin/nvidia-ctk"
 	}