Close stdios when fork/exec'ing virtmgr

Bug: 357611151
Test: a microdroid VM using the vm tool on adb shell.
Check the stdin/out/err of the virtmgr process. They are all /dev/null.

Change-Id: Ia71aff181402ace3b2b0861d22c04abf689fa08d
diff --git a/libs/libvmclient/src/lib.rs b/libs/libvmclient/src/lib.rs
index 7b576e6..fe86504 100644
--- a/libs/libvmclient/src/lib.rs
+++ b/libs/libvmclient/src/lib.rs
@@ -45,6 +45,7 @@
 use shared_child::SharedChild;
 use std::io::{self, Read};
 use std::process::Command;
+use std::process::Stdio;
 use std::{
     fmt::{self, Debug, Formatter},
     fs::File,
@@ -90,6 +91,9 @@
         let (client_fd, server_fd) = posix_socketpair()?;
 
         let mut command = Command::new(VIRTMGR_PATH);
+        command.stdin(Stdio::null());
+        command.stdout(Stdio::null());
+        command.stderr(Stdio::null());
         // Can't use BorrowedFd as it doesn't implement Display
         command.arg("--rpc-server-fd").arg(format!("{}", server_fd.as_raw_fd()));
         command.arg("--ready-fd").arg(format!("{}", ready_fd.as_raw_fd()));