Right now, this does not change anything, because backup ignores
max-chunk and max-workers.  However, as soon as backup is switched over
to block-copy for the background copying process, we will need it to
keep 129 passing.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210120102043.28346-1-mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>