Introduce a proper inc snapshot subcommand

[stgraber]

One bit of inconsistency that's always bothered me with LXD is that lxc snapshot and lxc restore are top level commands of their own. This makes it very awkward to allow for snapshot listing, renaming, ...

We've been wanting to fix this for years, but couldn't without breaking backward compatibility. As the fork doesn't pretend to be backward compatible at the CLI level, it's a good opportunity to fix that one.

[monstermunchkin]

Should there be a proper subcommand for managing storage volume snapshots as well?

[stgraber]

Yeah, I think we should do the same thing with lxc storage volume snapshot indeed.

[monstermunchkin]

I guess what we need is inc snapshot {create,delete,rename,copy,info,restore,list}. And the same for inc storage volume snapshot {create,delete,rename,copy,info,restore,list}.

inc rename (and inc move) and inc copy already support renaming and copying snapshots respectively. Should inc rename (and inc move) be limited to only support instances? I believe inc copy should keep some support for snapshots as one can do this: inc copy c1/snap0 c2. But we could drop snapshot to snapshot copying in inc copy.

Alternatively, this could be done in inc snapshot restore with a third positional argument like this:

inc snapshot restore c1 snap0 c2`

@stgraber what are your thoughts on this?

[stgraber]

Yeah, agreed on the new commands.

For rename/move we should remove the snapshot support.

Copy would keep it but indeed only for creating a new instance from a snapshot.

Support in delete would go away too.