Reland "vm tool: rename --gki arg to more generic --os one"

Test: presubmit
Bug: 333730505
Change-Id: I867bb2edeb9f5a285fdee59dae2366e3afeb707d
diff --git a/android/vm/src/main.rs b/android/vm/src/main.rs
index 81ca8fa..110e0ca 100644
--- a/android/vm/src/main.rs
+++ b/android/vm/src/main.rs
@@ -155,10 +155,10 @@
     #[arg(long)]
     devices: Vec<PathBuf>,
 
-    /// Version of GKI to use. If set, use instead of microdroid kernel
-    #[cfg(vendor_modules)]
+    /// Version of OS to use. If not set, defaults to microdroid.
+    /// You can list all available OSes via `vm info` command.
     #[arg(long)]
-    gki: Option<String>,
+    os: Option<String>,
 }
 
 impl MicrodroidConfig {
@@ -172,16 +172,6 @@
         }
     }
 
-    fn gki(&self) -> Option<&str> {
-        cfg_if::cfg_if! {
-            if #[cfg(vendor_modules)] {
-                self.gki.as_deref()
-            } else {
-                None
-            }
-        }
-    }
-
     fn devices(&self) -> &[PathBuf] {
         cfg_if::cfg_if! {
             if #[cfg(device_assignment)] {
diff --git a/android/vm/src/run.rs b/android/vm/src/run.rs
index 0e1f4cc..b07a472 100644
--- a/android/vm/src/run.rs
+++ b/android/vm/src/run.rs
@@ -140,11 +140,7 @@
         bail!("Either --config-path or --payload-binary-name must be defined")
     };
 
-    let os_name = if let Some(ver) = config.microdroid.gki() {
-        format!("microdroid_gki-{ver}")
-    } else {
-        "microdroid".to_owned()
-    };
+    let os_name = if let Some(ref os) = config.microdroid.os { os } else { "microdroid" };
 
     let payload_config_str = format!("{:?}!{:?}", config.apk, payload);
 
@@ -192,7 +188,7 @@
         memoryMib: config.common.mem.unwrap_or(0) as i32, // 0 means use the VM default
         cpuTopology: config.common.cpu_topology,
         customConfig: Some(custom_config),
-        osName: os_name,
+        osName: os_name.to_string(),
         hugePages: config.common.hugepages,
         boostUclamp: config.common.boost_uclamp,
     });