iotests: restrict 254 to support only qcow2

Test fails at least for qcow, because of different cluster sizes in
base and top (and therefore different granularities of bitmaps we are
trying to merge).

The test aim is to check block-dirty-bitmap-merge between different
nodes functionality, no needs to check all formats. So, let's just drop
support for anything except qcow2.

Reported-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190605155405.104384-1-vsementsov@virtuozzo.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
1 file changed