tests: send SIGTERM to kill GuestCommand

Killing CLH by SIGKILL will cause inaccurate code coverage
 information. This patch changes the signal to SIGTERM.

Fixes: #6507

Signed-off-by: Songqian Li <sionli@tencent.com>

test_infra/src/lib.rs

@@ -798,6 +798,17 @@ pub fn check_matched_lines_count(input: &str, keywords: Vec<&str>, line_count: u
     }
 }
 
+pub fn kill_child(child: &Child) {
+    let result = unsafe { libc::kill(child.id() as i32, libc::SIGTERM) };
+    if result != 0 {
+        eprintln!(
+            "Failed to kill child with SIGKILL: {:?}",
+            io::Error::last_os_error()
+        );
+        let _ = unsafe { libc::kill(child.id() as i32, libc::SIGKILL) };
+    }
+}
+
 pub const PIPE_SIZE: i32 = 32 << 20;
 
 static NEXT_VM_ID: Lazy<Mutex<u8>> = Lazy::new(|| Mutex::new(1));