tests/acceptance: Send <carriage return> on serial lines

Some firmwares don't parse the <Newline> control character and
expect a <carriage return>.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20191028073441.6448-5-philmd@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>

tests/acceptance/boot_linux_console.py

@@ -34,7 +34,7 @@ def wait_for_console_pattern(self, success_message):
                                  failure_message='Kernel panic - not syncing')
 
     def exec_command_and_wait_for_pattern(self, command, success_message):
-        command += '\n'
+        command += '\r'
         self.vm.console_socket.sendall(command.encode())
         wait_for_console_pattern(self, success_message)