Add a new tool: sanitize-config

This can be used for two purposes:

- safety copy of the config file, with just the secrets changed
- cleanup of the config file (full randomization), so that (e.g.) users
  could send a broken config file to the devel-list

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>