Add a new objectclass, ipaObject, that will add a UUID to many IPA objects

ipaObject is defined as an auxiliary objectclass so it is up to the
plugin author to ensure that the objectclass is included an a UUID generated.
ipaUniqueId is a MUST attribute so if you include the objectclass you must
ensure that the uuid is generated.

This also fixes up some unrelated unit test failures.

tests/test_xmlrpc/test_user_plugin.py

@@ -48,6 +48,7 @@ class test_user(XMLRPC_test):
         assert_attr_equal(res, 'sn', self.sn)
         assert_attr_equal(res, 'uid', self.uid)
         assert_attr_equal(res, 'homedirectory', self.home)
+        assert_attr_equal(res, 'objectclass', 'ipaobject')
 
     def test_2_user_add(self):
         """