Update for SSH design: Cluster name, ignore node daemon

While writing the initial version of this design I misunderstood what
“setup-ssh” does. It doesn't actually start the node daemon and just
configures SSH, nothing else.

This patch adds the cluster name as a field to the JSON structure and
clarifies the purpose of the node daemon certificate given.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>