python/qemu: rename command() to cmd()

python/qemu: rename command() to cmd()

Use a shorter name. We are going to move in iotests from qmp() to
command() where possible. But command() is longer than qmp() and don't
look better. Let's rename.

You can simply grep for '\.command(' and for 'def command(' to check
that everything is updated (command() in tests/docker/docker.py is
unrelated).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-id: 20231006154125.1068348-6-vsementsov@yandex-team.ru
[vsementsov: also update three occurrences in
   tests/avocado/machine_aspeed.py and keep r-b]
Signed-off-by: John Snow <jsnow@redhat.com>