Change lvm_type for cinder volume

Change default value 'lvm_type=auto' for cinder
backend

Change-Id: I6817c75c754700deaa90939cdcf77e20d9a5a334
Related-Prod: PROD-19687
diff --git a/README.rst b/README.rst
index 1914361..fbdaaf9 100644
--- a/README.rst
+++ b/README.rst
@@ -249,6 +249,17 @@
           # Add key without value to remove line from policy.json
           'volume:extend':
 
+Default Cinder backend lvm_type setup
+
+.. code-block:: yaml
+
+    cinder:
+      volume:
+        enabled: true
+        backend:
+          # Type of LVM volumes to deploy; (default, thin, or auto). Auto defaults to thin if thin is supported.
+          lvm_type: auto
+
 
 Default Cinder setup with iSCSI target
 
diff --git a/cinder/files/backend/_lvm.conf b/cinder/files/backend/_lvm.conf
index b71fa23..e305056 100644
--- a/cinder/files/backend/_lvm.conf
+++ b/cinder/files/backend/_lvm.conf
@@ -3,6 +3,8 @@
 host={{ backend.get('host', grains.host) }}
 volume_driver = cinder.volume.drivers.lvm.LVMVolumeDriver
 volume_backend_name={{ backend_name }}
-lvm_type = default
+{%- if backend.lvm_type is defined %}
+lvm_type = {{ backend.lvm_type }}
+{%- endif  %}
 iscsi_helper = tgtadm
 volume_group = {{ backend.volume_group }}
\ No newline at end of file