qcow2_format.py: use strings to specify c-type of struct fields
We are going to move field-parsing to super-class, this will be simpler
with simple string specifiers instead of variables.
For some reason, python doesn't allow the definition of ctypes variable
in the class alongside fields: it would not be available then for use
by the 'for' operator. Don't worry: ctypes will be moved to metaclass
soon.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Message-Id: <
20200606081806.23897-8-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>