docker.py is run during configure, and produces an error: No module
named 'pwd'.

Use a more portable and recommended alternative to lookup the user
"login name".

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230306122751.2355515-4-marcandre.lureau@redhat.com>