iotests.py: filter compression type out

iotests.py: filter compression type out

We want iotests pass with both the default zlib compression and with
IMGOPTS='compression_type=zstd'.

Actually the only test that is interested in real compression type in
test output is 287 (test for qcow2 compression type) and it's in bash.
So for now we can safely filter out compression type in all qcow2
tests.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20211223160144.1097696-11-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>