objectstore: Remove the two levels structure of volume directories
objectstore: Remove the two levels structure of volume directories

Make it plain in the top level for volumes.

This would break the compatibility with existing backups


medallia/convoy,rancher/rancher-volume,rancherio/volmgr,rancher/rancher-volume,rancher/rancher-volume,rancherio/rancher-volume,rancherio/rancher-volume,rancher/convoy,nickvanw/convoy,medallia/convoy,jinuxstyle/convoy,jinuxstyle/convoy,medallia/convoy,rancher/convoy,rancher/convoy,rancherio/volmgr,nickvanw/convoy,jinuxstyle/convoy,rancherio/volmgr,rancherio/rancher-volume,nickvanw/convoy