Print backtrace of microdroid_manager to kmsg

To track any possible bugs on microdroid_manager.

Bug: 258760809
Test: intentionally crash microdroid_manager and see console
Change-Id: I2359e59270a1c6c5efab2a6cb1e0727bb3c5743e

microdroid_manager/microdroid_manager.rc

@@ -1,6 +1,9 @@
 service microdroid_manager /system/bin/microdroid_manager
     disabled
+    # print android log to kmsg
     file /dev/kmsg w
+    # redirect stdout/stderr to kmsg_debug
+    stdio_to_kmsg
     setenv RUST_LOG info
     # TODO(jooyung) remove this when microdroid_manager becomes a daemon
     oneshot

microdroid_manager/src/main.rs

@@ -47,6 +47,7 @@ use rustutils::system_properties;
 use rustutils::system_properties::PropertyWatcher;
 use std::borrow::Cow::{Borrowed, Owned};
 use std::convert::TryInto;
+use std::env;
 use std::fs::{self, create_dir, File, OpenOptions};
 use std::io::Write;
 use std::os::unix::io::{FromRawFd, IntoRawFd};
@@ -152,6 +153,11 @@ fn get_vms_rpc_binder() -> Result<Strong<dyn IVirtualMachineService>> {
 }
 
 fn main() -> Result<()> {
+    // If debuggable, print full backtrace to console log with stdio_to_kmsg
+    if system_properties::read_bool(APP_DEBUGGABLE_PROP, true)? {
+        env::set_var("RUST_BACKTRACE", "full");
+    }
+
     scopeguard::defer! {
         info!("Shutting down...");
         if let Err(e) = system_properties::write("sys.powerctl", "shutdown") {