Introduce cinder:config to manage custom options

This cinder::config is aim to use cinder config resources
to manage custom configurations in cinder config files.

This will make end user easy to add their own custom options
in Hiera data.

Fully implements blueprint cinder-custom-config

Change-Id: I58faf3f4c76b2eb2077552036a239b60103ee965
RBD backend: use ensure_resource

In the case we want to declare more than one backend using RBD driver,
we have a resource dupplication which could be fixed by using stlib
functions.

Closes-bug #1294138
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

Change-Id: I1783540cd8218e8bafb4d0b860ca4c5992f35a19
Merge "RBD backend: use ensure_resource"