Tests environments (go test or manual testing) should always consider
the passed disks are root disks and should not rely on disk.IsRootDisk()
function. The reason is that this latter can return a false negative
when called in a busy system. However, returning a false negative will
only occur in a testing environment and not in a production, so we can
accept this trade-off for now.
PutObject on multiple-zone with versioning would not
overwrite the correct location of the object if the
object has delete marker, leading to duplicate objects
on two zones.
This PR fixes by adding affinity towards delete marker
when GetObjectInfo() returns error, use the zone index
which has the delete marker.
