Add Tests for Groups Volume APIs - Part 2

Generic volume groups support was added to Cinder in the
Newton release:
https://blueprints.launchpad.net/cinder/+spec/generic-volume-group

This is the 2nd patch that adds the tempest tests for generic
volume groups APIs in Cinder. It adds group_snapshots clients.
It adds tests for the following APIs:

  * create group snapshot
  * delete group snapshot
  * show group snapshot
  * list group snapshot

Change-Id: I21f07f7b3e8f22055e7978c0bf4aa01b80b493d9
diff --git a/releasenotes/notes/add-volume-group-snapshots-tempest-tests-840df3da26590f5e.yaml b/releasenotes/notes/add-volume-group-snapshots-tempest-tests-840df3da26590f5e.yaml
new file mode 100644
index 0000000..2ca6e5a
--- /dev/null
+++ b/releasenotes/notes/add-volume-group-snapshots-tempest-tests-840df3da26590f5e.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Add group_snapshots client for the volume service as library.
+    Add tempest tests for create group snapshot, delete group snapshot, show
+    group snapshot, and list group snapshots volume APIs.