terminal-util: Enable line wrapping in reset_terminal_fd()

The qemu seabios firmware disables serial console line wrapping. Let's
make sure we re-enable it again when we reset a terminal to some sane
defaults.

To avoid potentially blocking on writing to the terminal, we put it
in nonblocking mode and add a timeout of 50ms.

test/TEST-08-INITRD/test.sh

@@ -70,7 +70,7 @@ check_result_qemu_hook() {
     fi
 
     # Check if the shutdown initrd was executed at all
-    if ! grep -qE "^Hello from shutdown initrd\s*$" "$console_log"; then
+    if ! grep -q "Hello from shutdown initrd" "$console_log"; then
         derror "Missing 'hello' message from shutdown initrd"
         return 1
     fi