Add more contexts upon verifying APEX failure

I found this helpful while debugging.

Bug: N/A
Test: TH
Change-Id: Ia547dd83afbc4fffafebf2683c7136689abddb67
diff --git a/guest/microdroid_manager/src/main.rs b/guest/microdroid_manager/src/main.rs
index 8b676b8..d12bfd3 100644
--- a/guest/microdroid_manager/src/main.rs
+++ b/guest/microdroid_manager/src/main.rs
@@ -265,7 +265,7 @@
     // Verify the payload before using it.
     let extracted_data = verify_payload(metadata, saved_data.as_ref())
         .context("Payload verification failed")
-        .map_err(|e| MicrodroidError::PayloadVerificationFailed(e.to_string()))?;
+        .map_err(|e| MicrodroidError::PayloadVerificationFailed(format!("{:?}", e)))?;
 
     // In case identity is ignored (by debug policy), we should reuse existing payload data, even
     // when the payload is changed. This is to keep the derived secret same as before.