Adjust the ring_builder to use the inventory file

The ring builder was using the rpc_user_config.yml, but the
inventory file should be the source of all truth.

* Adjust to use json instead of yaml
* Adjust to use the vars as they appear in the inventory file.
Adjust sample configs for Swift

* Move rpc_user_config.d to conf.d
* Move the swift variables out of rpc_user_config
* Ensure the swift.yml inside conf.d is correct