Update unit test for data/forceschedulers

Add buttonName attribute in the expected element for the test

master/buildbot/test/unit/test_data_forceschedulers.py

@@ -113,6 +113,7 @@
                     'tablabel': '',
                     'type': 'nested'}],
     'builder_names': [u'builder'],
+    'button_name': u'Force Build',
     'label': u'defaultforce',
     'name': u'defaultforce'}