deploy: Add user only if not exists

This way, if Kamaki setup fails for some reason (after adding the
user) we can run snf-deploy again without having astakos complaining
about duplicate user email.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
deploy: Restart gunicorn after setting up Astakos

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>