Fix setting up overlay with nvidia files

- make them override (likely older version) in the task image
- fix resolving squashfs path

Fixes https://github.com/fepitre/golem-gpu-live/issues/8

runtime/init-container/src/init.c

@@ -2006,7 +2006,7 @@ int main(int argc, char **argv) {
         CHECK(mkdir("/mnt/gpu-files", S_IRWXU));
         CHECK(mount("/dev/vdb", "/mnt/gpu-files", "squashfs", MS_RDONLY | MS_NODEV, ""));
         CHECK(mount("overlay", SYSROOT, "overlay", MS_NODEV,
-                    "lowerdir=/mnt/image:/mnt/gpu-files,upperdir=/mnt/overlay/upper,workdir=/mnt/overlay/work"));
+                    "lowerdir=/mnt/gpu-files:/mnt/image,upperdir=/mnt/overlay/upper,workdir=/mnt/overlay/work"));
     } else {
         CHECK(mount("overlay", SYSROOT, "overlay", MS_NODEV,
                     "lowerdir=/mnt/image,upperdir=/mnt/overlay/upper,workdir=/mnt/overlay/work"));

runtime/src/vmrt.rs

@@ -116,12 +116,12 @@ pub async fn start_vmrt(
         cmd.arg("none");
     }
 
-    if Path::new(FILE_NVIDIA_FILES).exists() {
+    if runtime_dir.join(FILE_NVIDIA_FILES).exists() {
         cmd.arg("-drive");
         cmd.arg(
             format!(
                 "file={},cache=unsafe,readonly=on,format=raw,if=virtio",
-                FILE_NVIDIA_FILES
+                runtime_dir.join(FILE_NVIDIA_FILES).display()
             )
             .as_str(),
         );