Test coverage for compute flavor_manage policies

This commit adds test coverage for the flavor_manage policies,
which includes tests only for the non-deprecated policy actions:

* "os_compute_api:os-flavor-manage:create"
* "os_compute_api:os-flavor-manage:delete"

This commit also renames _create_flavor in rbac_base for compute
module to be public since it is consumed by other files. It also
adds a wait_for_resource_deletion call.

Change-Id: I632235a1d81488ecc8fb1e92f801415a08c7e778
diff --git a/releasenotes/notes/flavor-manage-rbac-tests-eb78439316d67ab2.yaml b/releasenotes/notes/flavor-manage-rbac-tests-eb78439316d67ab2.yaml
new file mode 100644
index 0000000..0fbf24f
--- /dev/null
+++ b/releasenotes/notes/flavor-manage-rbac-tests-eb78439316d67ab2.yaml
@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Add test coverage for the os-flavor-manage compute API, which includes
+    tests for the following policy actions:
+
+      * "os_compute_api:os-flavor-manage:create"
+      * "os_compute_api:os-flavor-manage:delete"