use deliverable object model to validate the release notes links

Add an extra check that there are no notes links for repos not related
to the deliverable.

Change-Id: I7f0fb614cff8ae38c907670da484c3c75599c7c0
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

openstack_releases/deliverable.py

@@ -257,6 +257,10 @@ class Deliverable(object):
         for name, repo in sorted(self._repos.items()):
             yield repo
 
+    @property
+    def known_repo_names(self):
+        return set(self._repos.keys())
+
     def get_repo(self, name):
         return self._repos[name]