block/backup: disable copy_range for compressed backup

block/backup: disable copy_range for compressed backup

Enabled by default copy_range ignores compress option. It's definitely
unexpected for user.

It's broken since introduction of copy_range usage in backup in
9ded4a011496.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190730163251.755248-3-vsementsov@virtuozzo.com
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Max Reitz <mreitz@redhat.com>