Fix flavor_rxtx_rbac

Updates flavor_rxtx to more thoroughly test policy enforcement
by
- making use of RbacMalformedResponse to ensure rxtx_factor
  is included in response body
- adding new flavor_rxtx tests

Currently, POST /flavors is not tested as that action also
enforces os-flavor-manage: create, which is admin-only by
default and would therefore fail due to conflicting policy
restrictions. This test will be added once multi-policy
support is available.

Change-Id: I7fb35212fc6bb817a2b04077c983865e1191f214
Closes-Bug: #1712725
diff --git a/releasenotes/notes/flavor-rxtx-d7aadbb32a9f232c.yaml b/releasenotes/notes/flavor-rxtx-d7aadbb32a9f232c.yaml
new file mode 100644
index 0000000..083d9b0
--- /dev/null
+++ b/releasenotes/notes/flavor-rxtx-d7aadbb32a9f232c.yaml
@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    test_flavor_rxtx_rbac now offers complete
+    coverage for the os-flavor-rxtx policy.