iotests: add copy-before-write: on-cbw-error tests
Add tests for new option of copy-before-write filter: on-cbw-error.
Note that we use QEMUMachine instead of VM class, because in further
commit we'll want to use throttling which doesn't work with -accel
qtest used by VM.
We also touch pylintrc to not break iotest 297.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
[vsementsov: add arguments to QEMUMachine constructor]
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>