Allow IMEX channels to be requested as volume mounts

This change allows IMEX channels to be requested using the
volume mount mechanism.

A mount from /dev/null to /var/run/nvidia-container-devices/imex/{{ .ChannelID }}
is equivalent to including {{ .ChannelID }} in the NVIDIA_IMEX_CHANNELS
envvironment variables.

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

cmd/nvidia-container-runtime-hook/main.go

@@ -129,8 +129,8 @@ func doPrestart() {
 	if len(nvidia.MigMonitorDevices) > 0 {
 		args = append(args, fmt.Sprintf("--mig-monitor=%s", nvidia.MigMonitorDevices))
 	}
-	if len(nvidia.ImexChannels) > 0 {
-		args = append(args, fmt.Sprintf("--imex-channel=%s", nvidia.ImexChannels))
+	if imexString := strings.Join(nvidia.ImexChannels, ","); len(imexString) > 0 {
+		args = append(args, fmt.Sprintf("--imex-channel=%s", imexString))
 	}
 
 	for _, cap := range strings.Split(nvidia.DriverCapabilities, ",") {