RBAC tests for image_size compute policy action.

Add RBAC tests related to the ``image_size`` compute policy action:
"os_compute_api:image-size".

Note that if Patrole is enhanced to test multiple policies
simultaneously, these policy actions can be combined with the related
tests from ``ImagesRbacTest`` class in the same file.

Change-Id: Ifcf83daa61741be3d694d07b85fcd5ac6f616f46
diff --git a/releasenotes/notes/image-size-rbac-tests-545e5ace0d88ab34.yaml b/releasenotes/notes/image-size-rbac-tests-545e5ace0d88ab34.yaml
new file mode 100644
index 0000000..c0340cf
--- /dev/null
+++ b/releasenotes/notes/image-size-rbac-tests-545e5ace0d88ab34.yaml
@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Add RBAC tests related to the ``image_size`` compute policy action:
+    "os_compute_api:image-size".