Add ratelimiting parameters to cinder::api

Cinder master now has proper support for ratelimitng via
the api-paste.ini.

This commit adds a configuration option based on
https://github.com/openstack/cinder/commit/2acb6f329bb404e224e525b946c0aa6cdc74040c

Change-Id: I2bdbd5d917baaeaa151471a8b20b2d7939fcf82a