CLI Command to get User-ID and Space-ID

While documenting search how to reindex a space (cli command), I came across the point that we need as parameters a user-ID and space-ID as parameters. But getting these ID's is, except when using a browser console and then only for non-home spaces the admin has access to, currently not possible.

Here is a proposal to get around this situation:
We need to implement a CLI command (similar to nslookup) that resolves:

* a user name to its ID and vice versa
* a space name to its ID and vice versa
* prints the home-space ID of a given user-ID

@micbar @fschade @butonic @kobergj
Maybe to add this to the `Infinite Scale Team Board`?