Code review comment for ~stgraber/simplestreams:master

For now we'll go with the same "lxd.tar.xz" for both VM and container images.

If we need to start distinguishing between the two down the line, we can simply list two different files, both of filetype "lxd.tar.xz" and simply have the combined hashes for containers on one and combined hashes for vms on the other and have them each point to a different tarball.

That wouldn't need any client change to work and wouldn't even need defining any new filetype or anything on the server side.