Reworked tests for addNodes().

The tests now create ImmutableNode objects to be added to the configuration.
A test that does not make sense any longer was removed. All tests for
addNodes() are now successful.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/branches/immutableNodes@1573222 13f79535-47bb-0310-9956-ffa450edef68