pbr 5.6.0

Fix issues with 'requires-python' and 'python-requires', plus some other
trivial clean up.

Change-Id: Ibc0257c052aa0e60293c37a6990dce18e97e7730
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

deliverables/_independent/pbr.yaml

@@ -198,5 +198,9 @@ releases:
     projects:
       - repo: openstack/pbr
         hash: 5150198c294802f82ddc7ed5765546653bc19adf
+  - version: 5.6.0
+    projects:
+      - repo: openstack/pbr
+        hash: d9f72421f6dca6e151f999dbbebd81cc36445704
 repository-settings:
   openstack/pbr: {}