The binary for object-store-cli pointed at https://github.com/teamhephy/dockerbuilder/blob/master/rootfs/Dockerfile#L34 is not the same one that the main branch at https://github.com/teamhephy/object-storage-cli produces.
The immediate issue we observed with it is that AWS regions added by teamhephy/object-storage-cli#2 and related PRs still can not be used by dockerbuilder.