cinder.conf either supports lvm or ceph backend, not both

Cinder can be configured to support either
lvm or ceph backend. Using both backends only enables lvm
as the ceph backend configuration is combined
with the lvm backend part via elif code.

Change-Id: I57e515cf7cdd6377d60bfbc45a889553ce87207a
Closes-Bug: #1654996

ansible/roles/cinder/templates/cinder.conf.j2

@@ -100,8 +100,9 @@ volume_driver = cinder.volume.drivers.lvm.LVMVolumeDriver
 volume_backend_name = lvm-1
 iscsi_helper = tgtadm
 iscsi_protocol = iscsi
+{% endif %}
 
-{% elif enable_ceph | bool and cinder_backend_ceph | bool %}
+{% if enable_ceph | bool and cinder_backend_ceph | bool %}
 [rbd-1]
 volume_driver = cinder.volume.drivers.rbd.RBDDriver
 rbd_pool = {{ ceph_cinder_pool_name }}