[Fix gate]: Cinder policy change handling in tests

Cinder policies are made more granular and now we need
to adjust the patrole tests to handle those changed policies.

This commit introduces a new flag so that we test the old
policies in stable branches and new one in Xena onwards.

Change-Id: I4be60e3e92704f8e55d3acdb0e025078ae5b21f1
diff --git a/releasenotes/notes/changed-cinder-policies-xena-feature-flag-4b799db683e2840f.yaml b/releasenotes/notes/changed-cinder-policies-xena-feature-flag-4b799db683e2840f.yaml
new file mode 100644
index 0000000..286c77f
--- /dev/null
+++ b/releasenotes/notes/changed-cinder-policies-xena-feature-flag-4b799db683e2840f.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Added new feature flag called ``changed_cinder_policies_xena`` under
+    the configuration group ``[policy-feature-enabled]`` for testing Cinder
+    tests withe old and new policies.