Fix repository_tool test to expect promiscuous delegation to work

A and B both delegating to C works and is OK.

We should probably add more testing for this, covering more
complex situations.

Signed-off-by: Sebastien Awwad <sebastien.awwad@gmail.com>

tests/test_repository_tool.py

@@ -1189,9 +1189,8 @@ def test_delegate(self):
     self.assertEqual(self.targets_object.get_delegated_rolenames(),
                      ['tuf'])
 
-    # Try to delegate to a role that has already been delegated.
-    self.assertRaises(securesystemslib.exceptions.Error,
-        self.targets_object.delegate, rolename, public_keys, paths, threshold,
+    # Try to delegate to a role that has already been delegated. Expect success.
+    self.targets_object.delegate(rolename, public_keys, paths, threshold,
         terminating=False, list_of_targets=list_of_targets,
         path_hash_prefixes=path_hash_prefixes)