Test clearing unknown autoclear_features by qcow2 on incoming
migration.

[ kwolf: Fixed wait for destination VM startup ]
Signed-off-by: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>