Introduce nova::config

Add a new class nova::config which allows the creation and
management of arbitrary nova_config and nova_api_paste_ini resources.

This will add the ability for the end user to use Hiera to manage
those resources.

Change-Id: Iad7a2b764884887a75f5f6db3e1660644e07c5c0
Closes-bug: #1290634
Merge "Introduce nova::config"