rune/libcontainer: Set the mode of sgx device to 0666

This is a regular setting.
Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

rune/libcontainer/specconv/example.go

@@ -180,7 +180,7 @@ func Example() *specs.Spec {
 				Source:      "/run/aesmd",
 				Options:     []string{"rbind", "rprivate"},
 			})
-		var mode os.FileMode = 0644
+		var mode os.FileMode = 0666
 		spec.Linux.Devices = append(spec.Linux.Devices,
 			specs.LinuxDevice{
 				Path:     "/dev/isgx",