node-daemon-setup: generate client certificate

node-daemon-setup: generate client certificate

So far, the client certificate of a node that is added
to the cluster was created in LUNodeAdd using an RPC
call. This is now simplified by creating the certificate
already in tools/node_daemon_setup.py and only retrieving
its fingerprint by RPC to add it to the configuration.

This simplifies the backend function from only reading
the fingerprint instead of creating the certificate.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>