This change updates ceph_client and os_cinder roles to allow
cinder-backup to use ceph. We also create a new group called
'cinder_backup' which allows us to only retreive the cinder backup key
if cinder-backup is actually in use.
To use, you would simply need to set cinder_service_backup_driver to
cinder.backup.drivers.ceph in your user_variables.yml file.
NOTE: You will need to update your
/etc/openstack_deploy/env.d/cinder.yml in order for this change
to execute successfully.
Change-Id: Ib94effa40208bbc8de0f78c5487316be007adcf1
Closes-Bug: #1481787
Implements: blueprint ceph-block-devices
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