Disable snapshot support in Cinder NFS backend by default

Currently there is a known issue[1] in snapshot feature of cinder nfs
backend, which causes data corruption in several cases.
This change makes the feature disabled by default to require some
consideration by users before enabling the feature.

Note that this change makes the default value in Tripleo consistent
with the one(False) in cinder, so also fixes the inconsistency about
the default values.

[1] https://bugs.launchpad.net/cinder/+bug/1860913

Related-Bug: #1860913
Closes-Bug: #1896324
Change-Id: I12b8a01d0b28fed66be8ae0b1723dd89f6dc00ff

deployment/cinder/cinder-volume-container-puppet.yaml

@@ -108,7 +108,7 @@ parameters:
       CinderEnableNfsBackend is true.
     type: comma_delimited_list
   CinderNfsSnapshotSupport:
-    default: true
+    default: false
     description: >
       Whether to enable support for snapshots in the NFS driver. Effective
       when CinderEnableNfsBackend is true.

releasenotes/notes/cinder-nfs-snapshot-support-disabled-2d2e08c97537bc94.yaml

@@ -0,0 +1,14 @@
+---
+fixes:
+  - |
+    The default value of CinderNfsSnapshotSupport has been changed from true
+    to false, to be consistent with the default value in cinder.
+
+upgrades:
+  - |
+    Since the default value of CinderNfsSnapshotSupport has been changed from
+    true to false, the parameter should be explicitly set when enabling
+    snapshot feature in cinder nfs snapshot support. Any users enabling the
+    feature should be aware of the known issue which can cause data corruption.
+    See `bug 1860913 <https://bugs.launchpad.net/cinder/+bug/1860913>`_ to
+    find more details.