Check for rbd as a default & optional glance back-end
Check for rbd as a default & optional glance back-end

Currently only the default back-end is checked. This patch
ensures that both the default and additional beck-ends are
checked.

Change-Id: I0bc50a03bc6ca6939bd842a197c383bd5ced7bd2
Closes-Bug: #1670556

robb-romans/openstack-ansible,bunchc/openstack-ansible,BjoernT/os-ansible-deployment,yanyao/openstack-ansible,cfarquhar/openstack-ansible,cfarquhar/openstack-ansible,yanyao/openstack-ansible,stackforge/os-ansible-deployment,openstack/openstack-ansible,cloudnull/os-ansible-deployment,stackforge/os-ansible-deployment,BjoernT/openstack-ansible,os-cloud/os-ansible-deployment,BjoernT/openstack-ansible,robb-romans/openstack-ansible,BjoernT/os-ansible-deployment,os-cloud/os-ansible-deployment,cloudnull/os-ansible-deployment,bunchc/openstack-ansible,BjoernT/os-ansible-deployment,openstack/openstack-ansible