More work on EFI boot records and kernel updates

src/hive_config.rs

@@ -35,7 +35,7 @@ pub struct HiveConfig {
 #[derive(Debug, Serialize, Deserialize)]
 pub struct KernelConfig {
     /// kernel cmd string that will be passed as kernel boot parameter.
-    cmd: String,
+    pub cmd: Option<String>,
 }
 
 #[derive(Debug, Serialize, Deserialize)]