test/py: log when tests send CTRL-C

Write a note to the log file when a test sends CTRL-C to U-Boot. This
makes it easier to follow what's happening in the logs, especially since
U-Boot doesn't echo the character back to its output, so there's no other
signal of what's going on.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

test/py/u_boot_console_base.py

@@ -212,6 +212,7 @@ class ConsoleBase(object):
             Nothing.
         '''
 
+        self.log.action('Sending Ctrl-C')
         self.run_command(chr(3), wait_for_echo=False, send_nl=False)
 
     def drain_console(self):