Switched from `gcutil` to `gcloud`.

`gcutil` has been deprecated in favor of `gcloud compute`:
https://developers.google.com/compute/docs/gcutil/
Target instance -> `localhost` for SSH endpoint.

For SSH forwarding, the `ssh` command syntax is

    `ssh -L [bind_address:]port:host:hostport [...]`

where the `host` is relative to the host we have connected to, which is
`${SERVER}` in this case. Thus, the simplest endpoint is `localhost`
since we don't need to make another hop.