Add script to benchmark new backup architecture.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210116214705.822267-24-vsementsov@virtuozzo.com>
[mreitz: s/not unsupported/not supported/]
Signed-off-by: Max Reitz <mreitz@redhat.com>