iotests: refactor some common qmp result checks into generic pattern

To simplify further conversion.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20231006154125.1068348-10-vsementsov@yandex-team.ru
Signed-off-by: John Snow <jsnow@redhat.com>
5 files changed