Rename "signature" to "metadata"

Bug: 186396424
Test: atest ApexTestCases MicrodroidHostTestCases
Change-Id: Id401d33edc6c6d4aba2b5982c8ab75820faea793
diff --git a/microdroid_manager/src/main.rs b/microdroid_manager/src/main.rs
index fbbe8f3..1ab17d5 100644
--- a/microdroid_manager/src/main.rs
+++ b/microdroid_manager/src/main.rs
@@ -15,8 +15,8 @@
 //! Microdroid Manager
 
 mod ioutil;
+mod metadata;
 mod payload_config;
-mod signature;
 
 use android_logger::Config;
 use log::{info, Level};
@@ -32,9 +32,9 @@
 
     info!("started.");
 
-    let signature = signature::load()?;
-    if !signature.payload_config_path.is_empty() {
-        let config = VmPayloadConfig::load_from(Path::new(&signature.payload_config_path))?;
+    let metadata = metadata::load()?;
+    if !metadata.payload_config_path.is_empty() {
+        let config = VmPayloadConfig::load_from(Path::new(&metadata.payload_config_path))?;
         if let Some(main_task) = &config.task {
             exec(main_task)?;
         }