Enable nfs driver volume snapshots by default

Change-Id: I36d7d62514416104c1f2f36cbd29c26c34c0d20d
Closes-Bug: #1733304

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

@@ -125,6 +125,7 @@ image_upload_use_cinder_backend = True
 volume_driver = cinder.volume.drivers.nfs.NfsDriver
 volume_backend_name = nfs-1
 nfs_shares_config = /etc/cinder/nfs_shares
+nfs_snapshot_support = True
 {% endif %}
 
 {% if enable_cinder_backend_hnas_iscsi | bool %}

releasenotes/notes/enable-nfs-volume-snapshots-a0347a31662b1109.yaml

+---
+features:
+  - |
+    This feature enables volume snapshots for NFS Cinder driver.
+    NFS volume snapshots appeared in Ocata release and require
+    libvirt >= 1.2.7
+upgrade:
+  - |
+    On upgrade NFS Cinder snapshots will be activated. One can
+    prohibit this by setting nfs_snapshot_support = False in
+    /etc/kolla/config/cinder/cinder-volume.conf, section '[nfs-1]'.
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