iotests: Add @error to wait_until_completed

Callers can use this new parameter to expect failure during the
completion process.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20191108123455.39445-5-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
1 file changed