iotests: Filter refcount_order in 036

iotests: Filter refcount_order in 036

This test can run just fine with other values for refcount_bits, so we
should filter the value from qcow2.py's dump-header.  In fact, we can
filter everything but the feature bits and header extensions, because
that is what the test is about.

(036 currently ignores user-specified image options, but that will be
fixed in the next patch.)

Signed-off-by: Max Reitz <[email protected]>
Reviewed-by: Maxim Levitsky <[email protected]>
Message-id: 20191107163708[email protected]
Signed-off-by: Max Reitz <[email protected]>