Unmanage and manage snapshots

This feature provides the ability to import/export volume snapshot
from one Cinder to another and to import snapshots that have not been
managed by Cinder from a storage back end to Cinder.

Added:
- Api for snapshot-unmange
- Api for snapshot-manage
- New client 'snapshot_manage_client'
- 'delete_snapshot' method
Note: Cinder V1 does not support unmanage & manage snapshot.

Change-Id: Ib02fe171b07814aa12d311171dceac834ecbfe39
diff --git a/releasenotes/notes/add-snapshot-manage-client-as-library-a76ffdba9d8d01cb.yaml b/releasenotes/notes/add-snapshot-manage-client-as-library-a76ffdba9d8d01cb.yaml
new file mode 100644
index 0000000..9a4e6b1
--- /dev/null
+++ b/releasenotes/notes/add-snapshot-manage-client-as-library-a76ffdba9d8d01cb.yaml
@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Define v2 snapshot_manage_client client for the volume service as
+    library interfaces, allowing other projects to use this module as
+    stable libraries without maintenance changes.
+
+    * snapshot_manage_client(v2)