Support Vault KV versions 1 and 2

[Southclaws]

The difference isn't obvious at all. I'm also not sure what APIs need to be used for v2.

There is some code in the vault CLI source: https://github.com/hashicorp/vault/blob/master/command/kv_helpers.go#L99

But none of it is exposed for importing for some reason. So this might require copying/implementing a v2 check.

It seems to manipulate the mount path that's being read: https://github.com/hashicorp/vault/blob/master/command/kv_get.go#L94-L110