Centralized oslo config management

OpenStack process tend to have many config options, and many hosts.
It is a pain to manage this tons of config options.
To centralize this management helps operation.

We can use chef or puppet kind of tools, however
sometimes each process depends on the other processes configuration.
For example, nova depends on neutron configuration etc

My idea is to have config server in oslo.config, and let cfg.CONF get config from the server.
This way has several benefits.

- We can get centralized management without modification on each projects ( nova, neutron, etc)
- We can provide horizon for configuration