iotests/197: Fix for compat=0.10

iotests/197: Fix for compat=0.10

Writing zeroes to a qcow2 v2 images without a backing file results in an
unallocated cluster as of 61b3043965.  197 has a test for COR-ing a
cluster on an image without a backing file, which means that the data
will be zero, so now on a v2 image that cluster will just stay
unallocated, and so the test fails.  Just force compat=1.1 for that
particular case to enforce the cluster to get allocated.

Fixes: 61b3043965fe3552ee2684a97e7cc809ca7a71b3
Signed-off-by: Max Reitz <[email protected]>
Message-Id: <20200727135237.1096841[email protected]>
Reviewed-by: Eric Blake <[email protected]>