tests/acceptance: Ignore binary data sent on serial console

If a guest sends binary data on the serial console, we get:

 File "tests/acceptance/avocado_qemu/__init__.py", line 92,
   in _console_interaction msg = console.readline().strip()
 File "/usr/lib64/python3.8/codecs.py", line 322,
   in decode (result, consumed) = self._buffer_decode(data, self.errors, final)
 UnicodeDecodeError: 'utf-8' codec can't decode byte 0xa9 in position 2: invalid start byte

Since we use the console with readline(), fix it the easiest
way possible: ignore binary data (all current tests compare
text string anyway).

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210515134555.307404-2-f4bug@amsat.org>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Tested-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>

tests/acceptance/avocado_qemu/__init__.py

@@ -86,14 +86,17 @@ def _console_interaction(test, success_message, failure_message,
     assert not keep_sending or send_string
     if vm is None:
         vm = test.vm
-    console = vm.console_socket.makefile()
+    console = vm.console_socket.makefile(mode='rb', encoding='utf-8')
     console_logger = logging.getLogger('console')
     while True:
         if send_string:
             vm.console_socket.sendall(send_string.encode())
             if not keep_sending:
                 send_string = None # send only once
-        msg = console.readline().strip()
+        try:
+            msg = console.readline().decode().strip()
+        except UnicodeDecodeError:
+            msg = None
         if not msg:
             continue
         console_logger.debug(msg)