Update glance::backend::rbd options

This patch is aim to add rbd options in glance-api.conf
and also update related spec test.

Fixes bug #1221074

Change-Id: Ifcbaf15ab4a7aedb074abac42941181e53d538c4
Merge "Update glance::backend::rbd options"
Merge git://github.com/puppetlabs/puppetlabs-glance