python/machine.py: change default wait timeout to 3 seconds

python/machine.py: change default wait timeout to 3 seconds

Machine.wait() does not appear to be used except in the acceptance tests,
and an infinite timeout by default in a test suite is not the most helpful.

Change it to 3 seconds, like the default shutdown timeout.

Signed-off-by: John Snow <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Cleber Rosa <[email protected]>
Tested-by: Cleber Rosa <[email protected]>
Message-Id: <20200710050649[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>